Bibliometric Analysis of Green Marketing Research from 1977 to 2020

: The scientiﬁc community’s growing interest in green marketing research can be traced through the abundance of published literature on the topic. However, there is still a lack of a comprehensive and systematic research focusing on the evolution of this ﬁeld. The main objective of this paper was to consolidate the state-of-the-art research on green marketing through a bibliometric study of articles published from 1977 to 2020, and to analyze and present the results from the perspective of growing trends in the ﬁeld; productive and inﬂuential countries, institutions, authors, articles, and research journals; keywords; authorship patterns; and international collaborations. The study results indicate a gradual increase in green marketing research from 1977 to 2020, more so in the last ﬁve years. A total of 1025 scholarly documents were published in 634 journals during this period and listed in the Web of Science (WOS). The top 10 most productive countries were then analyzed. A great number of institutions from both developing countries (in terms of article count) and developed countries (in terms of citation scores), were compared. Finally, based on keywords and a three-factor analysis, it was concluded that green marketing, sustainability, sustainable development, environment marketing and sustainable marketing have attracted extensive attention during the past decade as keywords. tions, and authors; key journals; authorship patterns; collaborative networks; three-factor analysis; and global collaboration patterns.


Introduction
Green marketing consists of all marketing activities designed and implemented to satisfy human needs in ways that do not have a negative impact on the environment [1]. Marketing is not simply sales and advertisements. It includes a broad range of additional activities such as product ideation, manufacturing, packaging, promotion and distribution. Similarly, green marketing incorporates a broad range of marketing activities that may include product design and redesign, green manufacturing and integrated marketing communication, etc. Green marketing is also termed as ecological marketing [2], sustainable marketing [3], eco marketing [4], enviropreneurial marketing [5,6] and environmental marketing [7,8]. Sustainable marketing is a term that commonly represents green marketing, even though sustainability as a concept can be controversial, open to multiple interpretations, and difficult to translate into meaningful actions due to the political, economic and technological constraints faced by companies and governments [9] (p. 752). Sustainability and sustainable marketing include three main elements: environmental, social, and economic [3], whereas green marketing mainly focuses on environmental factors. It starts with the consumers, has a long-term approach and involves complete utilization of a company's resources for innovation [10]. tions, and authors; key journals; authorship patterns; collaborative networks; three-factor analysis; and global collaboration patterns.
The following research questions have been formulated to achieve the objectives of the research: 1.
What were the publishing trends in green marketing from 1977 to 2020? 2.
Which journals have been frequently preferred by researchers for green marketing? 3.
Which of the countries, organizations, and authors have been most productive in green marketing research? 4.
Which authorship and collaborative patterns of research have been most common in green marketing research? 5.
Which keywords have been frequently used in green marketing research?

Method
The bibliometric analysis method was used to evaluate and identify the publishing trends and patterns in green marketing literature. Bibliometric is a quantitative/statistical method used to analyze publishing trends of research articles, conference papers, and other scholarly documents.

Database Selection
There are several renowned indexing and abstracting databases. Some are multidisciplinary (Scopus, WOS) while others are subject-specific databases (MEDLINE, PubMed, AGRICOLA, ERIC). Out of these databases, Scopus and WOS are both highly regarding all over the world. WOS was chosen for the purpose of this study as it is considered to be the most trusted, powerful, and reliable database in the world, and is guided by the legacy of Dr. Eugene Garfield, the inventor of the world's first citation index. The data were retrieved from the WOS authentic indexing and abstracting scientific database, containing quality academic work. Both the qualitative and quantitative aspects are covered in the current study. It is worth noting that some papers, which were indexed in other multidisciplinary and subject-specific databases, might have been missed during the process of data retrieval.

Search Query
The following search query was run in the topic field (TS) of the WOS core collection. The query was run on 19 June 2020, at Imam Abdulrehman Bin Faisal University, Saudi Arabia. TS = ("Green marketing" OR "ecological marketing" OR "eco* marketing" OR "sustainable marketing" OR "Environmental Marketing" OR "Enviro* Marketing").

Inclusion/Exclusion Criteria
The time frame for the publication search was automatically set in WOS from 1900 till 19 July 2020, with no limitations on language and year of publication. Double-extraction method was used. Two authors extracted the data and evaluated the study eligibility independently. The titles and abstracts of all acceptable papers were individually screened. The search yielded 1198 results which were then imported into an excel file. Four duplicated records were removed and the rest were further screened for relevance by excluding 169 irrelevant records consisting of reviews, notes, editorial materials, letters, short surveys, meeting abstracts, news items, or corrections. A total of 1025 records were then assessed for eligibility. No irrelevant records were identified at this stage ( Figure 1).

Data Analysis
This section presents the results of the bibliometric analysis of green marketing literature published during the period of the study. After screening each record by reading the title and abstract, 1025 records consisting of articles, review papers, proceeding papers, early access, and book chapters were selected for data analysis. It was found that these records/articles had been published in 634 journals, written by 2218 authors, affiliated with 1106 institutions based in 84 countries. Furthermore, they had received 18,140 citations. A total of 1013 had been published in the English language while only 12 were in other languages. In the study, the citation impact (CI), which describes the average citations received by specific publications, was calculated by dividing the total number of citations by a total number of publications. The CI illustrates the average number of citations that a specific publication has received. Additionally, certain terms such as U1, U2, and Z9, as defined by the WOS database, were used [27]. U1 refers to the usage count of a publication in the last 180 days. Usage count is defined by the WOS as the count of the number of times the full text of a record has been accessed or saved in the last 180 days. This count can fluctuate as the end date of the fixed period advances and is updated daily [28]. Since the data were retrieved on 19 July 2020, it would be the reference start date for the last 180 days. Similarly, U2 refers to the usage count since 2013, and Z9 refers to the total times cited count (cited in the WOS Core Collection, Arabic Citation Index, BIOSIS Citation Index, Chinese Science Citation Database, Data Citation Index, Russian Science Citation Index, SciELO Citation Index). Figure 2 shows the year-wise frequency of publications and citations of green marketing literature from 1977 to 2020. Some years are missing as no publication was recorded in 1978, 1979, 1981-1983, 1985, 1987-1988, and 1990. The number of publications and citations have significantly increased over the years. A boom in citations and publications on green marketing can be observed after 2012 and 2019, respectively. The most successful publication year was 2019, in which the highest (118) number of articles were published. On the other hand, the highest number of citations (2062) were seen in the year 2012.

Top Ten Publishing Countries
The top ten highly productive countries are shown in Table 1. It can be seen that the most productive country had produced over 200 publications, the top two countries had over 140 publications, and the top five countries in the list have produced over 50 publications during the period of the study. The results show that the United States of America (USA) has had outstanding productivity with 201 publications and 7072 citations; fol-

Top Ten Publishing Countries
The top ten highly productive countries are shown in Table 1. It can be seen that the most productive country had produced over 200 publications, the top two countries had over 140 publications, and the top five countries in the list have produced over 50 publications during the period of the study. The results show that the United States of America (USA) has had outstanding productivity with 201 publications and 7072 citations; followed by China with 146 publications and 1431 citations. However, the highest CI (50.52) was recorded for the United Kingdom (UK), despite having only 54 publications. Canada can be seen at the bottom of the list with only 27 publications.

Top Ten High-Research-Producing Institutions
The top 10 research-producing organizations are shown in Table 2. It is apparent that most of the organizations (n = 6) had 8 or 9 publications, whereas the top 2 organizations had 12 and 10 publications, respectively. The Bucharest University of Economic Studies, Romania, emerged as the most productive organization with 12 publications and 32 cita-

Top Ten High-Research-Producing Institutions
The top 10 research-producing organizations are shown in Table 2. It is apparent that most of the organizations (n = 6) had 8 or 9 publications, whereas the top 2 organizations had 12 and 10 publications, respectively. The Bucharest University of Economic Studies, Romania, emerged as the most productive organization with 12 publications and 32 citations, followed by the University of Leeds, England, with 10 publications, 649 citations, and a CI of 64.90. Tamkang University, Taiwan, had an impressive CI of 68.63 with only eight publications, while the same number of publications produced by The University Brawijaya, Indonesia, had the lowest CI of 1.13 with only nine citations.  Table 3 highlights the most prolific authors in green marketing literature. The study results showed that the publication range of authors varied from five to nine. "Chen YS" emerged as the most productive author with nine publications, 921 citations, and the highest h-Index, followed by "Kim J" with 7 publications (Table 3). Notably, four authors in the list had recently (2019) started contributing to the literature on green marketing and did not have any citations at the time of the study (TC = 0).  Table 4 highlights the top 10 research journals in green marketing literature. It shows that five journals had more than 10 publications. Seven out of the 10 top journals fell under the Quartile 1 category and the maximum number of journals (4) had been published from Netherlands. The journal "Sustainability" (MDPI) stands first in the table with 33 publications and 149 citations, followed by the Journal of Cleaner Production (Elsevier) with 22 publications and 746 citations. It is interesting to note that the "Journal of the Academy of Marketing Science", which has published only nine publications, had 907 citations and the highest impact factor of 9.36.

Most Cited Journals with Strongest Citation Burst
A citation burst is a useful analytic method used to identify articles that receive particular attention from relevant scientific communities during a certain time frame [29]. In other ways, it highlights the most active period of a document during which it garners maximum attention from the scientific community. Figure 4 represents the top 10 most cited journals with maximum citation bursts using CiteSpace software. The blue color represents the overall time period of the citation burst and red color represents the active time period of citation burst. It can be seen that three journals had a strength of seven or more based on their citation bursts. "Environment Marketing Strategy" (sr. no. 10) had the highest strength of 7.64 from 1996 to 2012 followed by "American Economy Review" (sr.    Figure 5 displays the authorship patterns in green marketing literature. It was found that the authorship pattern ranged from single author to a maximum of 13 authors. This shows that collaborative research is far more common than single authorship in green marketing literature (two and three authors). The top three authorship patterns included two authors with 334 publications, three authors with 257 publications, and single author with 241 publications.  Figure 5 displays the authorship patterns in green marketing literature. It was fou that the authorship pattern ranged from single author to a maximum of 13 authors. T shows that collaborative research is far more common than single authorship in gre marketing literature (two and three authors). The top three authorship patterns includ two authors with 334 publications, three authors with 257 publications, and single auth with 241 publications.

Keyword Analysis
A keyword analysis of the data informed us that 2346 different keywords had be used by green marketing authors during their research. A co-occurrence network of k words had been used with a minimum occurrence of seven keywords and 54 items co taining eight clusters, as shown in Figure 6. The size of the ball shows a strong network keywords and each color represents a separate cluster. It was observed that the top f keywords, i.e., green marketing, sustainability, sustainable development, environme and sustainable marketing, had a significant number of occurrences and this was evide in the total link strength.

Keyword Analysis
A keyword analysis of the data informed us that 2346 different keywords had been used by green marketing authors during their research. A co-occurrence network of keywords had been used with a minimum occurrence of seven keywords and 54 items containing eight clusters, as shown in Figure 6. The size of the ball shows a strong network of keywords and each color represents a separate cluster. It was observed that the top five keywords, i.e., green marketing, sustainability, sustainable development, environment, and sustainable marketing, had a significant number of occurrences and this was evident in the total link strength. Figure 7 shows the top 15 keywords used in green marketing research from 2001 to 2020. The figure has two distinct panels. The left keywords panel highlights data from 2001 to 2020, and the right panel covers keywords from 2016 to 2020. Both panels show that "green marketing" and "sustainability" were the prevailing topics in all green marketing areas of research. Furthermore, the right panel shows that the top five sub-areas from 2016 to 2020 were "green marketing", with 32 publications, followed by "sustainability" with 11 publications, "sustainable development" and "sustainable marketing" with 5 publications each, and "environmental marketing" with only three publications. Additionally, if we compare Figures 5 and 6, it becomes apparent that some new sub-areas of green marketing have appeared in the 21st century. For instance, the keyword "environment" on the fourth rank in Figure 5 is replaced by "sustainable marketing" in Figure 6.  to 2020, and the right panel covers keywords from 2016 to 2020. Both panels show that "green marketing" and "sustainability" were the prevailing topics in all green marketing areas of research. Furthermore, the right panel shows that the top five sub-areas from 2016 to 2020 were "green marketing", with 32 publications, followed by "sustainability" with 11 publications, "sustainable development" and "sustainable marketing" with 5 publications each, and "environmental marketing" with only three publications. Additionally, if we compare Figures 5 and 6, it becomes apparent that some new sub-areas of green marketing have appeared in the 21st century. For instance, the keyword "environment" on the fourth rank in Figure 5 is replaced by "sustainable marketing" in Figure 6.       Figure 8 presents the published literature on green marketing by focusing on the relationship among top keywords, authors, and sources. The results of the analysis identified the top authors in green marketing, preferred source for publications, and sub-areas of green marketing. Figure 8 shows that the top three authors, i.e., Chen YS., Kim J., and Do Pace A., and five sub-areas, i.e., green marketing, green, sustainability, environmental marketing, and marketing, had a strong relationship with green marketing itself. Furthermore, these authors preferred to publish in three sources, i.e., Journal of Business Ethics, Journal of Cleaner Production, and Journal of Global Scholars of Marketing Science.  Figure 9 shows the relationship among subject areas (keywords), sources, and countries on green marketing research. The top five subject areas, i.e., green marketing, sustainability, green, marketing, and sustainable marketing, had a relationship with five sources, i.e., Sustainability, Journal of Business Research, Journal of Cleaner Production, Journal of Business Ethics, and Business Strategy and The Environment. Furthermore, these subject areas had a strong relationship with the top two most productive countries, i.e., USA and China.   Figure 9 shows the relationship among subject areas (keywords), sources, and countries on green marketing research. The top five subject areas, i.e., green marketing, sustainability, green, marketing, and sustainable marketing, had a relationship with five sources, i.e., Sustainability, Journal of Business Research, Journal of Cleaner Production, Journal of Business Ethics, and Business Strategy and The Environment. Furthermore, these subject areas had a strong relationship with the top two most productive countries, i.e., USA and China.  Figure 9 shows the relationship among subject areas (keywords), sources, and countries on green marketing research. The top five subject areas, i.e., green marketing, sustainability, green, marketing, and sustainable marketing, had a relationship with five sources, i.e., Sustainability, Journal of Business Research, Journal of Cleaner Production, Journal of Business Ethics, and Business Strategy and The Environment. Furthermore, these subject areas had a strong relationship with the top two most productive countries, i.e., USA and China. Figure 9. Three-factor analysis of the relationship among keywords (left) sources (middle) and countries (right). Figure 9. Three-factor analysis of the relationship among keywords (left) sources (middle) and countries (right). Figure 10 shows the country collaboration map on green marketing literature. USA emerged as top collaborator with China (12 publications), followed by Canada and Korea (eight publications each), and India with the USA (six publications). There were six collaborations between UK and Cyprus. The least active among the 25 collaborators were Germany and Norway with only two publications.

Country Collaboration Map on Green Marketing Research
Publications 2021, 9, x FOR PEER REVIEW 15 of 21 Figure 10 shows the country collaboration map on green marketing literature. USA emerged as top collaborator with China (12 publications), followed by Canada and Korea (eight publications each), and India with the USA (six publications). There were six collaborations between UK and Cyprus. The least active among the 25 collaborators were Germany and Norway with only two publications.

Citation Bursts of Green Marketing Literature
Citation bursts present evidence that a specific publication is connected with a citation boom in a specific timeframe. Figure 11 presents the cited bursts of green marketing literature using CiteSpace software. The blue color represents the overall time period of the citation burst, light-blue color represents the citation bursts started after the year 2000 and red color represents the active time period of citation burst. The highest bursts were observed on the first (8)

Citation Bursts of Green Marketing Literature
Citation bursts present evidence that a specific publication is connected with a citation boom in a specific timeframe. Figure 11 presents the cited bursts of green marketing literature using CiteSpace software. The blue color represents the overall time period of the citation burst, light-blue color represents the citation bursts started after the year 2000 and red color represents the active time period of citation burst. The highest bursts were observed on the first (8)

Most Productive Countries, Authors, and Institutions and Publishing Trends
The results of the study show that the total number of publications from the top 10 most productive countries accounted for 65.9% of the total investigated publications on green marketing. These findings reflect the high interest of certain countries in green marketing research. Among them, USA had the maximum number of publications (201), and UK had the most influential publications (CI = 50.52). However, both the most productive institution and the most prolific author with the highest academic influence were surprisingly neither American nor British. Furthermore, even though USA had the highest number of total citations (TC = 7072), the CI of the country's publications was less than those of UK, Canada, and even Taiwan. One of the most interesting findings of the study is related to the top 10 productive organizations. It was found that only two institutions from Taiwan accounted for a collective CI of 133.74, and each institution had received more than 500 citations.
A growing interest was also found among academics regarding green marketing research. The number of published articles has been progressively increasing over the years, with a sharp increase in the last decade. Highest number of articles were published in the year 2019. This increase is consistent with the global trend in both corporate social responsibility (CSR) and sustainability research [30,31]. Typically, most of the influential articles were published between 2001 and 2012 [32][33][34]. Furthermore, during the last two decades, the literature on green marketing has extensively increased in terms of both knowledge creation and diversity in themes [35].
There has been a growing interest in social and environmental research over the past decade in the context of the developing countries as well [36]. Consequently, there has been an increase in the number of researchers and academicians working in the environmental related fields in these emerging and developing economies. Globalizations and the interconnectedness of international markets have also necessitated the establishment of regulatory frame works to oversee the actions of manufacturers and marketers working in these emerging economies, and to ensure their adherence to international guidelines.

Most Productive Countries, Authors, and Institutions and Publishing Trends
The results of the study show that the total number of publications from the top 10 most productive countries accounted for 65.9% of the total investigated publications on green marketing. These findings reflect the high interest of certain countries in green marketing research. Among them, USA had the maximum number of publications (201), and UK had the most influential publications (CI = 50.52). However, both the most productive institution and the most prolific author with the highest academic influence were surprisingly neither American nor British. Furthermore, even though USA had the highest number of total citations (TC = 7072), the CI of the country's publications was less than those of UK, Canada, and even Taiwan. One of the most interesting findings of the study is related to the top 10 productive organizations. It was found that only two institutions from Taiwan accounted for a collective CI of 133.74, and each institution had received more than 500 citations.
A growing interest was also found among academics regarding green marketing research. The number of published articles has been progressively increasing over the years, with a sharp increase in the last decade. Highest number of articles were published in the year 2019. This increase is consistent with the global trend in both corporate social responsibility (CSR) and sustainability research [30,31]. Typically, most of the influential articles were published between 2001 and 2012 [32][33][34]. Furthermore, during the last two decades, the literature on green marketing has extensively increased in terms of both knowledge creation and diversity in themes [35].
There has been a growing interest in social and environmental research over the past decade in the context of the developing countries as well [36]. Consequently, there has been an increase in the number of researchers and academicians working in the environmental related fields in these emerging and developing economies. Globalizations and the interconnectedness of international markets have also necessitated the establishment of regulatory frame works to oversee the actions of manufacturers and marketers working in these emerging economies, and to ensure their adherence to international guidelines.
Developing countries are the main suppliers and manufacturers of goods for the consumers in the developed world where social and environmental legal infrastructures are more robust; therefore, these manufacturers are compelled to adhere to policies set forth by the developed countries [37]. Compliance with local and international government regulations and industry standards has been the driving force behind the implementation of the environmental management systems in corporations working the developing world [38,39]. As a result of these social and environmental changes at the industrial and corporate levels, research related to social and environmental areas has also started gaining popularity among researchers in these emerging economies. The study results show that in the list of top 10 influential countries, six were developing or emerging economies, and three were from the Brazil, Russia, India, and China (BRIC) block. Seven out of 10 highly productive institutions were also from emerging economies and the first and third most influential authors also belonged to countries considered to be emerging economies.
Research on green marketing emerging from these developing economies also reflects the governmental interest towards sustainability. This is also in line with the sustainable development goals set forth by the United Nations (UN) in 2015 [40,41]. The environmental preservation is one of the major goals to be achieved by all nations as a long-term sustainability agenda laid out by the UN, along with certain economic and social factors [40]. Governmental funds, internal funding system of educational institutes, the corporate sector, and NGOs are the major funding sources for academic research in these countries [42] and, despite being independent, these funding bodies manage to work in close collaboration with each other on sustainability research. However, more work is needed in this regard, while Taiwan has managed to have a CI greater than that of USA, the rest of the five emerging economies (except India) had CI less than 10. The academic influence of these emerging economies (except Taiwan) is still weak. This might be due to the lack of international collaborations and/or the unavailability of the manuscripts.

Influential Journals in Green Marketing
Seven out of the 10 most preferred publication outlets for green marketing research are listed in the Quartile 1 (Q1) ranking of SSCI (Web of Science), four of these are from the Netherlands, and three are from USA. The Journal of Cleaner Production is ranked second with 22 articles and 746 total citations. Similarly, the Journal of Marketing has published 9 articles and is 2nd last in the list of highly influential journals. One out of those nine articles is ranked 3rd in the 10 most cited articles on green marketing [43]. Similarly, the Journal of Business Ethics has two highly cited articles on green marketing and is ranked third in the most influential journals with 18 articles, and the highest number of total citations. The Journal of Business Research is ranked fourth in the highly influential journals list and also has 1 article in the most cited article list. All these journals are from developed countries, follow a rigorous peer-review process and publish articles only in the English language. Secondly, the Journal of Marketing, Journal of Business Ethics, and Journal of Business Research are all specialized journals from the business category.

Authorship, Collaborative Patterns and, Frequently Used Keywords
Around 81.25% of the publications had three or fewer authors, and 23.5% were written by a single author. It should be noted that three of the 10 most influential articles were authored by one individual, three had two authors and two had four authors. Most collaborations were noted between the USA and China, and interestingly these two countries were one of the most influential countries in green marketing research as well. All top collaborations with developing countries including China, India, Cyprus, and Korea, were from USA.
International green marketing research collaborations are of paramount importance for all concerned. These collaborations help the collaborators in accessing technologies, knowledge, and resources, otherwise unavailable to them. They are also efficient and cost effective [44]. International collaborations help researchers maximize their citations [45].
According to the Royal Society, the articles with co-authors from five additional countries (in addition to the first author's country) received twice as many citations as compared to articles with no international collaborations [46]. The results of our analysis also support these findings.
The analysis identified top five keywords as "green marketing", "sustainability", "sustainable development", "environment", and "sustainable marketing". These keywords truly depict the essence of green marketing research. "Green consumerism", "green marketing mix", "green satisfaction", "consumer attitudes", and "green competitive advantage" were less researched keywords and represent the less considered sub-areas of green marketing. It has been observed that green consumerism, green satisfaction and green attitudes of consumers would need more attention in the future. The three-factor analysis of keywords, authors, and journals also identified the need for further investigating consumer behavior, environmental concerns, and green products.

Citations Bursts and Three-Factor Keywords Analysis
The papers that were highly cited were from varied journals such as the Journal of Marketing, Journal of Advertising, Journal of Business Ethics, Journal of Business Research, California Management Review, Management Science, Tourism Management, and International Journal of Operations and Production Management, and were published between 1995 and 2012. This finding indicates that seminal work was done on green marketing during this period. Henion's book "Ecological Marketing" received a significant number of citations in 2010-2011 [47]. Likewise, the highest citation burst was for Peattie's book "Environmental Marketing Management: Meeting the Green Challenge" from 2003-2013 [48]. In the results, top citation bursts started from 2000 and ended in 2015. These citation busts for green marketing literature identify its importance in the early 2000s, even though researchers were publishing in the area as early as 1971.
In the keywords analysis, it was found that authors from the USA and China had significantly used green marketing, sustainable marketing, and sustainability as keywords and had published in ISI impact factor journals including Sustainability, Journal of Business Research, Journal of Cleaner Production, Journal of Business Ethics, and Business Strategy and the Environment. All of these journals are highly respectable in the field of sustainability and green research. This finding highlights the importance of green marketing among authors, as well as editors of high impact journals, as an area of investigation. Researchers working in the green marketing area could focus on these journals as a possible outlet for their publications in the future. Similarly, our analysis also found greenwashing, ecological marketing, and sustainable consumption as promising emerging research areas for new researchers.

Limitations and Future Research Directions
Like all other bibliometric analysis studies, this study also had some limitations. Firstly, the analyzed data in the current study were downloaded only from WOS Core Collection database on a specific date; therefore, data from other databases collected at different times could have different results and conclusions [49]. Due to the WOS Core Collection database being the most authentic data source, we only focused on articles, conference papers, book chapters from WOS. Other databases may be incorporated (i.e., Scopus) to extend this work for a better understanding of research in green marketing. While the researchers endeavored to include all possible key terms to search and shortlist the articles for the study, however, the analysis could be extended by including more search terms as identified in the keywords cluster given in Figure 6.
Besides these limitations, the current investigation offers several prospective opportunities for future research. With this study, researchers from the green marketing area can design strategies focused on the topics (as shown by the visualization of data in this study) that are developing and have gained little attention in the previous investigations. In addition, they can find the most influential papers, authors, and journals to identify the research gaps and new insights in this area. Multiple avenues are possible for future research: future focus on more narrowed areas, i.e., green consumerism, green marketing mix, green satisfaction, consumer green attitudes, etc.; 4Ps (product, price, place, promotion) of green marketing can be investigated from a B to B and B to C market perspective; comparative research on green consumerism from developed and developing countries; and use of more comprehensive and broader demographic and psychographic variables. There are five notable predictions and trends that emerge from this study: research from developing and emerging economies; greenwashing; green consumerism; low-carbon economy; and eco-innovation.

Conclusions
The overall purpose of this study was to provide a comprehensive review of the research published on green marketing. Green marketing research is critical to promote sustainable consumerism in developed and developing countries. However, not a single bibliometric analysis has been completed that holistically reviews and summarizing the literature, progress, and future directions of this important sub-area of marketing as this study does for the period from 1977 to 2020.
Even so, based on our review and findings of the current study, we would like to suggest several prospective opportunities for future research. With this study, researchers working in the green marketing area can design strategies focused on the topics (as shown by the visualization of data in this study) that are developing. In addition, they can identify the most influential papers published, authors and journals in this area for identification of research gaps and new insights. For green marketing research trends and about the future insights, here are five notable predictions and trends from this study: research from developing and emerging economies; green washing; green consumerism; low-carbon economy; and eco-innovation. Similarly, based on the results of this bibliometric analysis, To conclude, this research has made an important contribution to the growing body of knowledge on green marketing research. By analyzing 1025 published articles, conference papers, and book chapters from WOS, we have provided new insights in the green marketing research area. Another important contribution of the current study is the inclusion of articles written in all languages. Results have shown that the academic interest in this area has gradually increased from 1977 to 2020.