Tourism towards Sustainability and Innovation: A Systematic Literature Review

: In this paper, we analyze the progress of tourism towards sustainability and innovation through a systematic literature review summarizing the last ﬁve years of research strictly focused on innovation and sustainability applied to tourism. This research comprises a range of theories, practices, methods, and results pursuing innovation and sustainability across different levels, stages, and drivers, and in many tourism contexts. Wide, in-depth, and structured analysis, evaluation, and examination (using the PRISMA and VOSviewer tools) of a ﬁnal sample of 50 scholarly papers from 27 journals, published between 2017 and the ﬁrst quarter of 2021, were undertaken. Current publications emphasize qualitative, quantitative, and mixed research methods, as well as statistical and econometric methods, such as descriptive statistics, factor analysis, and structural equation modeling. This study categorizes the four major topics identiﬁed, sustainability, innovation, sustainable development, and sustainable tourism, which comprised the contextual dimensions and relevant stages of the subject areas examined. This systematic literature review highlights advances and the signiﬁcantly increasing overall number of papers over recent years. Currently, sustainability is in a more advanced state compared to innovation. The outcomes highlight that the indicators of sustainability and innovation still need further analysis within the tourism context. However, more concrete process indicators are needed for continuous improvement of the front-end of innovation and sustainable tourism. The results help in better understanding the sustainability and innovation process as applied to tourism. In particular, this study explores further direct linkages between sustainability and innovation and tourism, discussing and providing new future directions aligned with the closing remarks as well as a strategic agenda for future action post-COVID-19


Introduction
Sustainable tourism is defined by the United Nations World Tourism Organization (UNWTO) [1] as being linked to the environmental, economic, and socio-cultural aspects underlying tourism development.In addition, the UNWTO, by advocating a suitable balance between these three established dimensions, aims to ensure the long-term sustainability of tourism.Sustainable tourism has emerged with the intent of reducing the accumulated damage and negative effects of tourism activities [2].To decrease negative tourism effects, the UNWTO [3] announced that 2017 would be the year of sustainable tourism, taking into account the sustainable development goals (SDGs) of the UN as applied to tourism; namely, the UNWTO [4] journey to 2030.As a result, several guidelines for the future development of sustainable tourism are given, providing the main environmental indicators for the tourism sector, which include climate change mitigation, pollution reduction, the use of renewables, and waste disposal [3].Sustainable tourism issues require special attention and have been addressed by several studies (e.g., [5,6]).Knox-Hayes, Chandra, and Chun [7] (p. 1) state that" sustainability is not a fixed endpoint, but rather a constantly evolving process of negotiation within and across societies".
Tourism is recognized as one of the fastest growing and developing and most dynamic worldwide industries.Tourism research on sustainability has been highlighted as a worldwide challenge [8].Sustainable tourism is currently of the utmost importance [9].Nowadays," the current COVID-19 outbreak and high risks of future pandemics have given rise to new challenges for sustainable tourism development" [9] (p. 1).Bearing this in mind, it can be inferred that planning and developing tourism purposefully, sustainably, and in terms of the emerging and cutting-edge issues, challenges, policies, and strategies has great significance and impact.
Tourism has been acknowledged as one of the most significant economic sectors in the major countries of the world.According to the World Travel and Tourism Council [10], in 2018, the travel and tourism sector experienced growth of 3.9%, outpacing that of the global economy (3.2%) for the eighth consecutive year.Over the past 5 years, one out of every five jobs was created by the sector, making travel and tourism the best partner for governments to generate employment [10].
This study addresses a critical gap regarding the need for an extensive and systematic literature review (SLR) covering recent years that analyzes and evaluates the role and impact of sustainability and innovation along with the worldwide tourism industry.The current research aims to deliver guidelines for further research through the identification of new insights and challenges for the strengthening of sustainable and innovative tourism.This study suggests that it is essential to rethink a new, global approach to sustainable and innovative tourism, which would lead to a powerful path forward in the future.To our knowledge, this is the first study to demonstrate the combined use of these two dimensions-sustainability and innovation-specifically extending their scope into a tourism setting because an intersection such as this has not been addressed before in the tourism area.The main goal addressed in this study is to assess the current degree of recent tourism research in sustainability and innovation, while taking into account several perspectives, contexts, applications, and drivers, through an SLR.With this purpose in mind, the specific objectives that follow from the main goal pointed out are as follows: to determine whether sustainability is more advanced than innovation or whether innovation is more advanced than sustainability in tourism, and to analyze whether sustainability and innovation are simultaneously associated in tourism.The methodology adopted consisted of an SLR covering the period from January 2017 up to March 2021, in which, as a final sample, 50 papers were selected from 27 journals and retrieved from the Scopus, Web of Science, and Science Direct online databases according to some key criteria; namely, titles, abstracts, keywords, subject areas, and the quality of the research carried out (evaluated using the citation history).Therefore, this study covers a more focused period but, in contrast, involves a broader spectrum than most studies.
In this study, based on the dominant research topics, we noticed that ultimate, key issues of innovative and sustainable tourism development were addressed and consolidated.Innovative and sustainable tourism has experienced rapid growth, which has had an impact on the creation of innovative and increasingly sustainable paradoxes, strategies, approaches, challenges, opportunities, solutions, and stakeholder potential in the tourism sector.This study includes qualitative, quantitative, and mixed studies that are synthesized with existing results to show the entire range of features, insights, drivers, indicators, and dimensions focused upon.However, despite the existing research highlighted in this systematic literature review, the indicators of sustainability and innovation still need to be better understood in terms of their association with the tourism context.This SLR advances knowledge focused on the prioritization of innovative and sustainable tourism projects, best practices, benchmarking, strategic planning, and implementation.The paper is structured as follows: first, an SLR focused on sustainability and innovation in tourism experiences is undertaken; then, its bibliometric results are explained; finally, the conclusions, the implications for researchers, managers, governance, and policymakers, and future research directions are presented.

Methodology
An SLR was performed in this study, as regards the research method, using the PRISMA protocol (Preferred Reporting Items for Systematic Reviews) [11].The PRISMA method allows for the identification and selection of scientific papers with higher quality and impact and is comprised of four stages: (1) identification, (2) screening, (3) eligibility, and (4) inclusion [11].The PRISMA flow diagram was carefully followed and applied in this SLR, as shown in Figure 1.Therefore, regarding the methodology, four major steps were involved, namely the process description analysis (identification), the paper selection process (screening), the identification of sustainability and innovation towards tourism (eligibility), followed by the inclusion of the papers.The first step was a keyword search in the three most renowned databases, namely Scopus, Web of Science, and Science Direct, to gather dominant literature sources on sustainability and innovation in tourism, as a part of this procedure.In the second stage of the procedure, each indicator, each dimension, and each factor related to sustainability and innovation was examined and also evaluated for whether they directly and/or indirectly influenced the tourism industry.Given this, to reach a consensual solution, our results are subsequently presented, compared, and discussed.
Initially, 301 papers relating sustainability and innovation associated with the tourism context were identified in the above-mentioned databases, selected by a structured keyword search.Namely, the following dimensions were used to conduct the literature search: sustainability AND innovation AND tourism.The period of 4 years and 3 months was chosen because UNWTO [3] announced the year 2017 as the year of sustainable tourism, taking into account the SDGs set out by the United Nations (UN), applied to tourism regarding the UNWTO [4] journey to 2030.Thus, this period catches a range of papers presenting the evolution of the sustainability and innovation literature towards tourism.According to Alderson et al. [12], seven inclusion criteria were specified with the intent to proceed systematically.
The chosen papers were thus the subject of a thorough and detailed selection process.The objective was to ensure the reliability and representativeness of the results presented, obtaining a comparable body of research in terms of the innovation and sustainability of tourism fields and disciplines.In searching within peer-to-peer reviewed journals, we also sought guidance from their rankings and the noteworthy number of citations and publishers' popularity.
The tourism sustainability and innovation literature was based on seven inclusion criteria, as follows: (1) being available in one of the three mentioned databases and cited in at least one of the relevant papers; (2) comprised of two of the keywords, namely "sustainability/sustainable" and "tourism" or "innovation/innovative" and "tourism" or three keywords including "sustainability/sustainable" and "innovation/innovative" and "tourism" in the title, abstract or/and full text; (3) peer-reviewed papers; (4) journal publications; (5) published between 2017 and the first quarter of 2021; (6); papers in the English language; and (7) papers considering the process or practices of tourism sustainability and innovation.
set of papers was accessed on 31st March 2021.
To generate and assure a transparent process, either one or two of the tourism sustainability and innovation dimensions as well as the underlying factors of the identified study were presented.Therefore, as expected, the current review process is both scientific and replicable.In effect, any study whose main constructs and keywords were not directly focused on sustainability and innovation for the tourism industry was eliminated, as demonstrated in the PRISMA logical flow diagram of the SLR (Figure 1).As a basis for the subsequent bibliometric analysis, a Microsoft Excel database was filled in including the indicator-related information, such as: the year of publication; number of publications; journal; location of investigation; citation count; quantitative, qualitative, and mixed nature research methods as well as statistical and econometric methods used for the data analysis.

Bibliometric Analysis
Through the bibliometric analysis, one may see that there is a growing number of released publications, with 2020 being the best year of the period considered.The year 2021, from which we only considered three months, is understandably at a lower level.Taking into account the research criteria, 301 potential papers were identified, and 23 duplicate papers were eliminated.Consequently, 228 papers were eliminated due to their less adequate titles, abstracts, and article content, according to a more detailed analysis (e.g., the text did not refer to the theme tourism and/or innovation and/or sustainability).Therefore, the final sample counted 50 papers in which the research covers in greater depth the sustainability and innovation in tourism theme.The systematic literature review was thus focused on a final set of 50 papers from the Scopus, Web of Science, and Science Direct online databases, from 27 refereed academic journals, which were properly collected and analyzed, from January 2017 to the first quarter of 2021.Thus, this set of papers was accessed on 31st March 2021.
To generate and assure a transparent process, either one or two of the tourism sustainability and innovation dimensions as well as the underlying factors of the identified study were presented.Therefore, as expected, the current review process is both scientific and replicable.In effect, any study whose main constructs and keywords were not directly focused on sustainability and innovation for the tourism industry was eliminated, as demonstrated in the PRISMA logical flow diagram of the SLR (Figure 1).
As a basis for the subsequent bibliometric analysis, a Microsoft Excel database was filled in including the indicator-related information, such as: the year of publication; number of publications; journal; location of investigation; citation count; quantitative, qualitative, and mixed nature research methods as well as statistical and econometric methods used for the data analysis.

Bibliometric Analysis
Through the bibliometric analysis, one may see that there is a growing number of released publications, with 2020 being the best year of the period considered.The year 2021, from which we only considered three months, is understandably at a lower level.2020 is thus an especially strong year, accounting for a higher number of publications than the sum of 2017 through 2019.
In terms of publication per journal, Figure 2 makes evident a wide dispersion of published research.There is a very wide range of journals with only one or two publications.On the other hand, two journals stand out from the group, each with nine published papers: Journal of Sustainable Tourism and Sustainability, which points out to a higher degree of specialization on the theme of sustainability and innovation in tourism.2020 is thus an especially strong year, accounting for a higher number of publications than the sum of 2017 through 2019.
In terms of publication per journal, Figure 2 makes evident a wide dispersion of published research.There is a very wide range of journals with only one or two publications.On the other hand, two journals stand out from the group, each with nine published papers: Journal of Sustainable Tourism and Sustainability, which points out to a higher degree of specialization on the theme of sustainability and innovation in tourism.In terms of publication per journal, Table 1 shows a wide dispersion of published research.In terms of publication per journal, Table 1 shows a wide dispersion of published research.Table 2 focuses on the geographical origin of the studies.In this case, the large majority of them were multinational studies, which means that they are publications that surveyed multiple countries.Besides the multinational approach, only Spain stands out as an individual location with eight studies.All of the other countries range from one to two studies/publications.As shown in Figure 3, a majority of over 60% of the publications cited between 60 to 100 references.There were also 4% that only used between zero and 20 references, while 6% used more than 140 references.
As shown in Figure 3, a majority of over 60% of the publications cited between 60 to 100 references.There were also 4% that only used between zero and 20 references, while 6% used more than 140 references.In Figure 4, regarding an assessment of the statistical and econometric approaches used in these publications, we see that almost 60% use only a descriptive approach, which entails a lower degree of complexity in the analysis.A total of 23% followed structural equation modeling and 18% used factor analysis.In Figure 4, regarding an assessment of the statistical and econometric approaches used in these publications, we see that almost 60% use only a descriptive approach, which entails a lower degree of complexity in the analysis.A total of 23% followed structural equation modeling and 18% used factor analysis.Qualitative approaches were chosen by 58% of the sample, contrasting with only 24% quantitative and 18% mixed.
VOSviewer software was used to determine the mapping of the strength of the cooccurrence links between keywords.In addition, this software allows you to visualize the existing connection networks between several of the most cited bibliometric dimensions.Thus, in this study, it can be inferred that from the total of all the keywords used by the authors in the articles, previously analyzed, eight keywords present a strong association between them (as shown in Figure 6); i.e., this is the set of keywords that simultaneously most often appears in the keywords presented.Figure 5 analyzes the research method that was used in the research publications.Qualitative approaches were chosen by 58% of the sample, contrasting with only 24% quantitative and 18% mixed.VOSviewer software was used to determine the mapping of the strength of the cooccurrence links between keywords.In addition, this software allows you to visualize the existing connection networks between several of the most cited bibliometric dimensions.Thus, in this study, it can be inferred that from the total of all the keywords used by the authors in the articles, previously analyzed, eight keywords present a strong association between them (as shown in Figure 6); i.e., this is the set of keywords that simultaneously most often appears in the keywords presented.
As expected, according to the SLR performed, the four dimensions most highlighted are sustainability, innovation, sustainable development, and sustainable tourism (Figure 6).Consequently, a significant link strength, of equal distance, of sustainability with sustainable development and sustainable tourism is of note.Moreover, it follows that the greatest link strength (bigger nodes and thicker line) is that of sustainability with innovation, but also of equal distance.Regarding the analysis of the mapping of the strength of the co-occurrence of common keywords between titles and abstracts using the VOSviewer software (Figure 7), ten keywords were found and recognized as the most reported in the entire sample of selected articles.In addition, the following four dimensions stand out, namely study, innovation, tourism, and sustainability, which represent a stronger association both in titles and in abstracts, with very similar distances between them.
There is a significant, interconnected network of keywords and groups of keywords that occur together.Looking closer at the interconnected network of  As expected, according to the SLR performed, the four dimensions most highlighted are sustainability, innovation, sustainable development, and sustainable tourism (Figure 6).Consequently, a significant link strength, of equal distance, of sustainability with sustainable development and sustainable tourism is of note.Moreover, it follows that the greatest link strength (bigger nodes and thicker line) is that of sustainability with innovation, but also of equal distance.
Regarding the analysis of the mapping of the strength of the co-occurrence of common keywords between titles and abstracts using the VOSviewer software (Figure 7), ten keywords were found and recognized as the most reported in the entire sample of selected articles.In addition, the following four dimensions stand out, namely study, innovation, tourism, and sustainability, which represent a stronger association both in titles and in abstracts, with very similar distances between them. i.
The destination keyword has a connection with the keywords factor, model, sustainability, study, innovation, tourism, and article.j.
Finally, the article keyword has a connection with the keywords factor, destination, model, tourism, study, sustainability, and innovation.
To summarize the VOSviewer analysis, the results fully corroborate the previous prediction continually advanced throughout the in-depth review of the articles.

Results
This section is divided into three subsections: sustainability in tourism, innovation in tourism, and categories of sustainability and innovation in tourism.This section thus focuses on the latest research in these topic areas.

Sustainability in Tourism
Font and McCabe [13] summarized the latest research on the breadth of theories, paradoxes, approaches, challenges, methods, and results of sustainability in tourism.The objective was to achieve more sustainable outcomes regarding mainstream sustainability into the wider tourism business sphere.Globally, "there are many innovative solutions to sustainability challenges and that there is a growing impetus for the development of more sustainable tourism products that can be marketed successfully" [13] (p. 11).Managers' sustainability attitudes lead to sustainable behavior [14].
Garay, Font, and Pereira-Molinerc [15] (p.418) addressed the understanding of sustainability behavior through the relationship between information acquisition, proactivity, and performance in 408 tourism enterprises in Catalonia (Spain), and the two main results are as follows: "(1) sustainability implementation is related to communication with other stakeholders, to the use of collective and formal channels, and the perceived usefulness of information; and (2) sustainability performance is related to the introduction of environmental and economic practices, to the use of both industry and broader sources of information, and the perceived usefulness of information".It is suggested that sustainability training and education be a part of the success in achieving behavior change in their target audiences.There is a significant, interconnected network of keywords and groups of keywords that occur together.Looking closer at the interconnected network of Figure 7 (10 clusters and 40 links): a.
The design methodology approach keyword has a connection with the keywords originality value, model, innovation, study, sustainability, and tourism keywords.b.
The originality value keyword has a connection with the keywords design methodology approach, model, factor, and sustainability.c.
The model keyword has a connection with the keywords design methodology approach, originality value, factor, study, innovation, sustainability, tourism, article, and destination.d.The innovation keyword has a connection with the keywords design methodology approach, model, sustainability, model, tourism, factor, article, and destination.e.
The study keyword has a connection with the keywords design methodology approach, model, innovation, sustainability, factor, tourism, destination, and article.f.
The sustainability keyword has a connection with the keywords originality value, design methodology approach, innovation, model, study, tourism, article, and destination.g.
The factor keyword has a connection with the keywords model, study, innovation, tourism, destination, and article.h.The tourism keyword has a connection with the keywords design methodology approach, originality value, model, study, innovation, sustainability, factor, destination, and article.i.
The destination keyword has a connection with the keywords factor, model, sustainability, study, innovation, tourism, and article.j.
Finally, the article keyword has a connection with the keywords factor, destination, model, tourism, study, sustainability, and innovation.
To summarize the VOSviewer analysis, the results fully corroborate the previous prediction continually advanced throughout the in-depth review of the articles.

Results
This section is divided into three subsections: sustainability in tourism, innovation in tourism, and categories of sustainability and innovation in tourism.This section thus focuses on the latest research in these topic areas.

Sustainability in Tourism
Font and McCabe [13] summarized the latest research on the breadth of theories, paradoxes, approaches, challenges, methods, and results of sustainability in tourism.The objective was to achieve more sustainable outcomes regarding mainstream sustainability into the wider tourism business sphere.Globally, "there are many innovative solutions to sustainability challenges and that there is a growing impetus for the development of more sustainable tourism products that can be marketed successfully" [13] (p. 11).Managers' sustainability attitudes lead to sustainable behavior [14].
Garay, Font, and Pereira-Molinerc [15] (p.418) addressed the understanding of sustainability behavior through the relationship between information acquisition, proactivity, and performance in 408 tourism enterprises in Catalonia (Spain), and the two main results are as follows: "(1) sustainability implementation is related to communication with other stakeholders, to the use of collective and formal channels, and the perceived usefulness of information; and (2) sustainability performance is related to the introduction of environmental and economic practices, to the use of both industry and broader sources of information, and the perceived usefulness of information".It is suggested that sustainability training and education be a part of the success in achieving behavior change in their target audiences.
In a broad SLR, Streimikiene et al. [9] addressed the sustainable tourist development challenges, and new insights were provided, namely: products and services, new kinds of tourism, customers' clusters, and profiles (mainly the elderly and disabled), green tourism services, sustainable consumption, and social tourism.Elmo et al. [17] focused their SLR (between 2015 and 2020) on sustainability in tourism as an innovation driver, highlighting the limitation of sustainability within tourism family businesses.The main results of this study demonstrate that innovative strategies have been poorly implemented, but conversely, some variables guaranteed the application of sustainable practices.
Karagiannis and Metaxas [19] have linked the relationship between tourism and sustainability in wine-related enterprises in Greece and reveal that wine tourism, as a touristic cluster, is still in an infant sustainability stage.These authors proposed nine sustainable development goals achieved through wine and food tourism in a region, with the proposed sustainable management tools, namely: (1) safety and health; (2) education; (3) equality/accessibility; (4) climate action/water and waste management; (5) protecting and enhancing cultural heritage, local identity, and assets; (6) economic growth; (7) industry and infrastructure; (8) responsible consumption; and (9) partnership for sustainability.
It is assumed that green technologies at tourist destinations integrate corporate social responsibility.Moreover, technology-based eco-innovation has a positive role and impact on sustainable development goals, in the context of sustainability and smart tourism applied to nonprofit organizations, with a positive tourist experience contribution [21].Technological innovation (cluster 1), firms' contributions in developing countries (cluster 2), non-financial reporting (cluster 3), and education for SDGs (cluster 4) are recognized as the main four interrelated research themes of SDGs applied in the business sector, through a bibliometric approach and SLR methods examined extensively [22].Knox-Hayes, Chandra, and Chun [7] proposed an analytical sustainability model applied in Iceland, through sustainable values and consisting of six major categories, namely: values (social and cultural value, value of natural and human capital, and value of future generations), agents (the government, businesses, NGOs and the general public), industries (fisheries, tourism, agriculture, renewable energy and technology, and services), challenges (meaning, awareness, and threats), opportunities (vision, development, and social change), and strategies (education, optimizing, adaptative planning, innovation, and green technologies).In turn, these authors found that values are fundamental for sustainable development as well as for being socially and environmentally interactive.Furthermore, the outcomes have proven that policies and practices impact values, so their model is circular and responsive rather than the classic linear model.
Tritto [23] proposed a new taxonomy and framework featuring items of tangible and intangible heritage, namely tailored to the context of world heritage sites, filling in this previously addressed gap related to environmental management practices.Based on the results of twenty-five interviews and a survey of 124 hotels to examine environmental management practices performed in this study, it showed that budget hotels, which use significantly less environmental management practices, prevail within both heritage sites' boundaries (tangible and intangible heritage).From another perspective, "guesthouses and boutique hotels adopt a range of environmental management practices that blend technology and traditional knowledge, and they are more likely to try to engage customers.The determinants for adoption are often individual values or exchanges of information with actors that include traditional heritage businesses" [23] (p.1).
López et al. [24] proposed a model of sustainable tourism in archaeological sites through a qualitative and quantitative approach, revealing that market orientation and innovativeness have a positive and direct impact on tourism sustainability.Dias et al. [25] developed sustainable business models, taking into account local knowledge acquisition and tourism lifestyle entrepreneurship.They have proven that there is a direct relationship between tourism lifestyle entrepreneurs' businesses and sustainable business models, which provide differentiation, competitiveness, and sustainability.Fennell and Bowyer [26] (p. 6) developed the tourism and sustainable transformation framework applied to tourism food consumption, integrating four stages, namely: "(1) preparation (preparing for the transformation), ( 2) transformations (action of transforming the system using multiple transitions), and (3) support (supporting the new transformed system to ensure success)", and (4) it is "configured to be holistic and flexible enough to apply to different sectors and niches within any industry" [26] (p. 6).
Henche, Salvaj, and Cuesta-Valiño [27] proposed a sustainable management model for cultural, creative, and historic tourism ecosystems.Unlike previous studies, this new model adds the role of small business associations and the collaboration of networks of stakeholders to support the coexistence of the private and public sectors and sustainable governance models.
Flores and Medeiros [28] proposed a framework of sustainability management applied to the wine industry, involving a total of nine countries (Brazil, France, Italy, Spain, South Africa, Australia, New Zealand, USA, and Chile), supporting and enhancing the internalization of sustainability principles in this sector.The Baccus framework is structured over five dimensions (environment, economic, social, political-institutional, and territorial), four guidelines (management, articulation and cooperation, innovation and learning, sustainability), and whereby 18 topics unfolded (water; air; wastewater; waste; energy; biodiversity; agricultural practices; production and operations; management systems; diversification; internal public; territory; community; governance; territorial articulation; players' coopetition; knowledge; and patrimony, landscape and cultural valorization), as a new framework process to enhance sustainability management in the wine industry.
Raub and Martin-Rios [29] developed a framework entitled the multi-stakeholderfilter model, translating the UN SDGs into actionable dimensions and subsets in the context of hospitality companies with maximum local impact.This framework is based on a seven-step process: (1) relevant SDGs, (2) identity stakeholders, (3) catalysts and obstacles, (4) implementation probability index, (5) select high impact SDGs, (6) sustainable business practices, and (7) leverage resources.
Seraphin and Tan [30] adopted a management approach regarding resort mini-clubs due to the fact that children are the future tourists, thus educating them to respect destinations.In this regard, the three-domain model of sustainable tourism education in resort mini-clubs are as follows: local context understanding; functional dimension; SDGs 4 and 12; and empowering, creative, and family-orientated fun.
Some organizations join voluntary sustainable tourism associations, using institutional theory to achieve several positive implications for both membership and sustainability monitoring systems [31].
Agyeiwaah, McKercher, and Suntikul [32] identified a set of seven core indicators of sustainable tourism: (1) job creation, (2) business viability, (3) quality of life, (4) water quality, (5) waste management, (6) energy conservation, and ( 7) maintenance of community integrity.To progress and to make a stake in sustainable tourism, 30 indicators for smart coastal destinations are considered, covered by six dimensions: (1) smart governance, (2) smart environment, (3) universal access, (4) smart business, (5) smart technology, and (6) smart innovation [33].Toivonen (2020) explored the Finnish population concerning space tourism and sustainability and their findings resulted in four dimensions: (1) virtual travel, (2) comparative fairness, (3) technological innovations, and (4) ecopolitics, based on the current emergence of planning strategies towards sustainability actions in space tourism.Crespi-Vallbona and Mascarilla-Miró [34] advocate street art as a sustainable tool in the context of mature tourist destinations, specifically the case of Barcelona.Their research supported a sustainable tourism governance model between a set of networks, such as the public sector, private businesses, cultural associations, and the general public.These authors found six key factors behind sustainable tourism management in mature destinations such as Barcelona, namely: (1) participation, (2) hedonism, (3) knowledge, (4) local identity, (5) tasting, and (6) nostalgia.
According to Oliveras-Villanueva, Llach, and Perramon [35], the number of scientific papers in global terms on sustainable practices in the hospitality sector, concerning business development, demonstrates a growing trend.Their findings shed light on three features, namely: (I) the five critical factors of sustainable success that affect service quality in the hospitality sector: (1) environmental factors, (2) business factors, (3) human factors, (4) motivational and customer factors, and (5) relational factors; (II) the ten main practices that companies perform to improve their quality of sustainable services in the hospitality sectors are: (1) the 3Rs (reduce, reuse, recycle), (2) ecological concern, (3) sustainability in internal operations, (4) increased quality and reduction in costs, (5) sustainable organizational learning, (6) sustainability and effective cost management, (7) sustainable food, (8) environmental certifications, environmental monitoring, (9) social practices, (10) sustainability in human resources; and (III) the analysis of critical factors regarding environmental practices and quality of service [35] (pp.11-12).
Pérez-Pineda, Alcaraz, and Colón [36] identified sustainable initiatives recognized as "sustainability-champion" hotels in the Dominican Republic, taking into account the views of key stakeholders.It was proven that most international hotels are engaging more actively in present-oriented strategies, namely pollution prevention and also in product/service stewardship.In addition, in the future-oriented strategy context, hotels (in general) show higher commitment to both clean technology and innovation, focusing on sustainability (as a growth path).
Tourism seasonality is one of the factors limiting the sustainable development of rural areas, due to the alternating peak and valley periods entailed by seasonality, considering their associated negative impacts, in terms of economic, environmental, or social terms that, in some situations, conditions the success of private and public policies and specific strategies to reduce seasonality [37].
Recent research concluded that "lifestyle entrepreneurs in rural tourism, although facing many constraints related to rural context and small dimension of the company, present relatively well-succeeded businesses that contribute to increased sustainability of the territories where they are located" [38] (p.223).Furthermore, it is also shown that the creation of sustainable entrepreneurial ecosystems is triggering throughout lifestyle entrepreneurs' characteristics.
Through the assessment of the key determinants of sustainability practices and policy adoption in small-and medium-sized tourism accommodation firms, results attest that the collaboration of tourism firms, employee culture, technological infrastructure, tourism intermediary's sustainability practices, and top management support have a significant impact on sustainable practice adoption, whereas government sustainable tourism policy and the locals' attitude toward sustainability have an insignificant impact [39] (p.94).

Innovation in Tourism
The situation recently experienced involving the COVID-19 pandemic has limited sustainable innovation in the development of all initial plans that sought to investigate in depth the situation with prestigious entities for sustainable development in Spain.Recent studies show that a large part of the population shows interest and concern for a change to improve the tourist situation in Spain as a potential sustainable tourist destination of international standing [40].The COVID-19 outbreak has hampered the development of sustainable innovation in the tourism sector despite the advances made in recent years by tourism policies.Consequently, it is essential to persist in raising awareness and social education, to enhance potential tourist destinations as a sustainable reference at the international level [40].As Crespi-Vallbona and Mascarilla-Miró [34] (p. 1) stated, "tourism is one of the activities most urgently in need of innovation... to keep the boom going", and to better understand how mature destinations and tourism managers devise innovative daily practice solutions.
In their SLR, related to green innovation for sustainable tourism, Satta, Spinelli, and Parola [41] confirmed the already expected growing interest focused on this research area, with the intent to continuously help drive value creation by "greener" and also more eco-friendly initiatives and sustainable strategies, by both tourist companies and tourism destinations.Sharma, Chen, and Liu [42] performed a systematic review related to eco-innovation in hospitality research, covering the analysis of 403 studies published in 13 established hospitality journals, resulting in a unified conceptual framework covering a total of seven research domains regarding eco-innovative practices: (1) eco-efficient strategy, (2) green consumerism, (3) CSR (corporate social responsibility) and outreach, (4) carbon management, (5) eco-labels (green certifications and standards), ( 6) management and employee engagement, and (7) analysis and evaluation.
Reyes-Santiago, Sánchez-Medina, and Díaz-Pichardo [43] developed a theoretical model to link the compatibility of the four types of organizational culture based on the competing values framework (CVF) (i.e., hierarchy, clan, market, and adhocracy culture) to different modes of eco-innovation, in two ways: radical-incremental and componentarchitectural.The results imply and point out that an adhocracy culture and organization size largely explain the presence of eco-innovation in the context of the hospitality industry in Mexico, facilitating the implementation of eco-innovation at different levels.Kuščer, Mihalič, and Pechlaner [44] established a comparative analysis of Austria, Slovenia, and Switzerland, and they developed the three-dimensional mountain destination innovation model (MDIM), attesting that tourism development depends on a destination's innovation levels, taking into account the socio-cultural, natural, political, legal, and technological environments.
Horng et al. [45] developed a new integrated theoretical model of sustainability innovations of eco-friendly hotels comprising innovation diffusion, environmental marketing strategy, sustainability innovations, and the organizational environment.This model was tested by 367 managers of eco-friendly hotels in Taiwan, and it offers support across three dimensions of hotels' sustainable innovation, namely: (1) diffusion of innovations, (2) environmental marketing strategy, and (3) sustainability innovations.Green innovation, through environmental regulations, green innovation strategy, and green organizational culture as antecedents, positively influences the sustainability performance (social, environmental, and economic) of the hotel industry [46].
Eco-innovations that directly contribute to reducing carbon emissions in the travel industry fulfill the goal of helping to advance sustainable tourism transitions integrated in a process of collaborative co-production.In addition, it is argued that eco-innovation is better understood when there is equal analytical treatment research among human and non-human elements that perform eco-innovations [47].
Business model innovation (BMI) directly contributes to sustainability in the tourism and hospitality field, with tourists seeking tourism activities towards innovative and sustainable themes [48].
In the context of wildlife tourism, Bertella [49] challenged the basic assumptions regarding sustainable tourism, and as an alternative proposed the innovation concept for a critical rethinking based on the adoption of the animal ethics lens, in quite a radical way.
Paunović et al. [50] extracted two major tourism destination clusters-developed ones and less developed ones-regarding the development of a sustainable destination, laying a foundation for differentiated theories of destination governance for both developing and developed destinations.
Garay, Font, and Corrons [51], analyzing sustainability-oriented innovation in tourism, conducted an analysis based on the decomposed theory of planned behavior, involving more than 300 accommodation establishments located in Catalonia (Spain) relating to water-related innovations.Moreover, the study results show how the innovation literature explains the attitudes, social norms, and perceived behavioral controls of the managers, explaining 56% of the sustainability behavioral intentions.
Using a sample with a total of 974 small and medium-sized German hotels and 62,766 independent reviews, Koch, Gerdt, and Schewe [14] examined the relationship between innovativeness, managers' sustainability attitudes as well as sustainable firm behavior.The model tested reveals that innovativeness and sustainability attitudes lead to sustainable behavior.
Triantafillidou and Tsiaras [52] explored innovation and tourism while considering a Greek sustainability perspective and advocate that sustainable innovation triggers sustainable entrepreneurship, establishing the relationship among sustainable tourism, innovation, and entrepreneurship, due to the fact that tourism is the most prominent sector of the economy in this country, without devaluing the role of local communities in the competitive sustainability dimension.
In archaeological sites, López et al. [24] have concluded that innovativeness (technological innovation and organizational innovation) positively and significantly influences tourism sustainability.Another perspective is pointed out by Foronda-Robles, Galindo-Pérez-de-Azpillaga, and Fernández-Tabales [33], advocating that smart innovation comprises one of the core indicators of sustainable tourism.
According to Palmi and Lezzi [53], tangible and intangible resources derived from tradition in the agritourism sector are recognized as drivers for innovation, particularly place identity.Consequently, Palmi and Lezzi [53] argue that the process of sustainable innovation (management, processes, marketing, and products and services) can be generated from a recombination of sources of tradition (firm, specific period, past industry, and destination).
Bressan and Pedrini [54] examined sustainability-oriented innovation (SOI) practices among micro and small firms operating in the tourism and hospitality sectors.The research findings indicate that there are different forms of SOI practice implementation through owners/managers/entrepreneurs in their day-to-day lifestyle motivation in conducting business, leading to the implementation of a set of specific technologies (water softeners to reduce laundry water usage, rainwater collection systems to reduce the environmental impact of guests, composting of organic waste and waste management practices based on the recycle/reuse approach.Hence, the adoption of this innovation ensures the offering to customers of an innovative mixture of tradition and modernity strongly contributing to the sustainability of micro and small tourism firms.From another perspective, the innovation of tourism firms has a significant impact on sustainability practice adoption in small-and medium-sized tourism accommodation firms [39].Warren, Becken, and Coghlan [55] (p. 1) argue that SOI in tourist accommodation providers requires "an innovative transition from "unsustainable" tourism and innovative research methods to develop theory and concepts for a sustainable tourism".Underlying findings recommend an SOI model (effective learning, formal education, and collaborations), recognizing innovation as a human-tohuman organic process.
For Loureiro [56], the only answer for continued sustainable tourism growth lies in processes of innovation and technology.Thus, for innovation to contribute to sustainable tourism growth, the following greener solutions and priorities are noteworthy: pre-book visits and parking space system; online payment; tourist sites; tourist real-time communication; connection among destination management authorities, operators, and public services operators; and environmentally compliant destinations.
Herrero Amo and De Stefano [57] discussed and combined the promoting of publicprivate partnerships (PPPs) as a feasible innovative approach to increase sustainable tourism, with a strong dependence on partners' local interest alignment including the adequacy of the social and economic partnership conditions, in developing tourism destinations.For Dias et al. [25], entrepreneurial communication has the strongest positive and direct impact on the innovativeness of tourism lifestyle entrepreneurs, including their associated self-efficacy.
Despite the conceptual, political, and operational articulation of innovation tourism being recognized as a difficult task to accomplish, Nunes and Cooke [58] argue for new global tourism innovation in a post-COVID-19 context, proposing the requalification of the role of innovation, the reconceptualization of the relationship between tourism and innovation, and the assessment of the previous relationship mentioned integrating a set of challenges, but in the post-COVID-19 phase.

Categories of Sustainability and Innovation in Tourism
The two sections above relating the SLR of the sustainability and innovation concepts in tourism produce valuable and usable insights.Specifically, the main ordered associated categories of these two constructs, visible in Table 3, show that sustainability and innovation are linked and connected.In fact, the categories of both concepts are directly and indirectly related.Moreover, it can be inferred that innovation (8 categories) is still in a less developed stage compared to sustainability (12 categories) in the tourism field, as sustainability is more addressed and examined than innovation by the most active scholars and researchers.
In the total of the top twenty categories identified, concerning sustainability and innovation, there are five common direct terms in both, namely: (1) technology, (2) eco/green, (3) sustainable, (4) practices, and (5) behavior.

Conclusions
The number of articles on these topics, namely sustainability and innovation related to tourism, although not particularly high, does demonstrate a growing trend.Despite this growth, however, there is an untreated line of research which was detected, namely the theme of innovation and sustainability in tourism.
As analyzed and concluded previously, guaranteeing sustainable and innovative tourism implies that stakeholders in the tourism industry continuously adopt sustainable and innovative practices to fulfill the improvement of service differentiation leading to higher levels of cooperation, growth, and progress in terms of visitor attractiveness and loyalty in the future.
Upon strict scrutiny of the systematic literature review conducted, which involved fifty research papers published over the last five years, this analysis focuses on the applicability of sustainability and innovation within the tourism domain.Currently, it can be inferred that there has been more scientific research carried out on sustainability applied to tourism than on innovation.Moreover, there are very few papers that simultaneously address sustainability and innovation associated with tourism.However, the findings also indicate that innovation is becoming increasingly associated with sustainability practices.
In addition, sustainability and innovation, from various perspectives, and regarding several applications and types, no longer represent a trend but a permanent and lifelong requirement for tourism.Not only in the present but even more so in the future, innovation and sustainability are undoubtedly considered as new triggers as well as drivers for tourism to position itself competitively in the global market.
This systematic literature review represents a pioneering attempt to analyze, explore, and evaluate the current body of literature on sustainability and innovation linked to tourism in the worldwide paradigm, having resulted in several new valuable insights, from the present and into the future.Indeed, the COVID-19 pandemic put the world on an effective path to combat the permanent pressure of sustainable change, which has long been acclaimed.Sustainability and innovation and their growing link to tourism, after the COVID-19 outbreak, will be unstoppable worldwide, bearing in mind that tourist activity is a sign of global peace and continued prosperity.
Regarding limitations, a few papers published in 2021, according to the selection and evaluation criteria, were not yet available for download.Other important future research involves interrelated studies that, in particular, cross the sustainability and innovation dimensions, to ensure the expected balance between them over the upcoming years.
Through the bibliometric analysis, one may see that there is a growing number of released publications, with 2020 being the best year of the considered period.The year 2020 is an especially strong year, accounting for a higher number than the sum of 2017 through 2019.
In terms of publication per journal, two journals stand out from the group, each with nine published papers: Journal of Sustainable Tourism and Sustainability, which points to a higher degree of specialization on the theme of sustainability and innovation in tourism.
Regarding the geographical origin of the publications, the vast majority of them surveyed multiple countries.Besides the multinational approach, only Spain stands out as an individual location with eight publications.
VOSviewer software was used to visualize the existing connection networks between several of the most cited bibliometric dimensions.
We also identified, regarding the total top twenty categories discussed above, concerning sustainability and innovation, five common direct terms in both: (1) technology, (2) eco/green, (3) sustainable, (4) practices, and (5) behavior.The above emphasizes the importance of technology, even in this realm, and that of behavior, as sustainability is basically about behavior and innovation will depend on the welcoming and acceptance of innovation."The foundation [ . . .] of every social science, is evidently psychology.A day may come when we shall be able to deduce the laws of social science from the principles of psychology" [59].Human beings, and the understanding of their actions, will rely on us understanding, above all, basic behavioral principles.
The way sustainability started to be implemented in tourism, after the proclamation of the SDGs by the UN-applied to tourism since 2017 and integrated in the UNWTO journey to 2030-is what effectively distinguishes this period studied (the last 5 years) from the previous one, due to the fact that the tourism industry has come under scrutiny since then, in global accordance with the wide variety of studies cited in this SLR.
Images of polluted regions having improved due to the COVID-19 lockdown have also turned viral on the Internet.Never before has tourism been under such pressure to be sustainable, as concerns the environment and innovative, whereby we humans continuously search for new experiences [60].
Hence, there is an emerging need for advanced new insights following this current research.This section closes with a remark for reflection: how can the sustainable tourism experience be enhanced?In fact, in the current paradigm of the sustainable tourism experience, the co-creation of different sustainable tourist segments is mandatory in the present and even more so in the future.

Figure 5
Figure5analyzes the research method that was used in the research publications.Qualitative approaches were chosen by 58% of the sample, contrasting with only 24% quantitative and 18% mixed.

Figure 5
Figure5analyzes the research method that was used in the research publications.Qualitative approaches were chosen by 58% of the sample, contrasting with only 24% quantitative and 18% mixed.VOSviewer software was used to determine the mapping of the strength of the cooccurrence links between keywords.In addition, this software allows you to visualize the existing connection networks between several of the most cited bibliometric dimensions.Thus, in this study, it can be inferred that from the total of all the keywords used by the authors in the articles, previously analyzed, eight keywords present a strong association between them (as shown in Figure6); i.e., this is the set of keywords that simultaneously most often appears in the keywords presented.
Figure 7 (10 clusters and 40 links):a.The design methodology approach keyword has a connection with the keywords originality value, model, innovation, study, sustainability, and tourism keywords.b.The originality value keyword has a connection with the keywords design methodology approach, model, factor, and sustainability.c.The model keyword has a connection with the keywords design methodology approach, originality value, factor, study, innovation, sustainability, tourism, article, and destination.d.The innovation keyword has a connection with the keywords design methodology approach, model, sustainability, model, tourism, factor, article, and destination.

Table 2 .
Number of publications per location where the survey was conducted.

Table 3 .
Summary of the sustainability and innovation categories.