http://www.mdpi.com/journal/materials/special_issues/mof/ Dear Colleagues, In recent years several metallorganic frameworks (MOFs) have been deeply investigated for their properties and potential application in catalysis, gas storage, ion exchange, separation, and polymerization. The main properties of MOFs are ordered structures, the presence of channels or cavities with defined shapes and dimensions, a large surface area, and in some cases, a peculiar lattice flexibility. Due to these properties, MOFs are very attractive materials for their potential applications, as compared to "classic" porous materials, such as zeolites and active carbons. MOFs can be considered as three-dimensionally structured coordination metal complexes, in which the metal ions are connected to the ligands through covalent coordination bonds. The key to their success is the appropriate design of molecular building blocks (linkers, connectors, counter-ions, etc.), to obtain the desired structure and physico-chemical properties. For example, N-, O-, and S-donor ligands are suitable candidate building blocks for the obtainment of unique structural motifs, that can show not only a great aesthetic and conceptual appeal, but also attractive functional properties. The MOFs described in the recent literature can be divided into the following classes: i) porous materials containing solvents, or other neutral or ionic guest species,whose porous structure irreversibly collapses upon their removal (1st generation MOFs), ii) materials with a stable, rigid, and robust framework, that remain unchanged after the removal of the guests (2nd generation MOFs), and iii) flexible structures able to adapt themselves to a modification, or removal, of guest species or to external stimuli, by a reversible change of the shape and dimensions of pores, or, more generally, of the geometrical parameters of their crystal lattice (3rd generation MOFs). Silvia Bordiga, Ph.D. Guest Editor Related Special Issue Metal Organic Frameworks in International Journal of Molecular Sciences {snippet name="submission_info"}