SummaryThe first part of this overview on functional materials for gas storage is mainly focused on environmental applications, which include the separation and capture of carbon dioxide and air purification where adsorbent materials play a decisive role to remove a large diversity of toxic compounds. The exploitation of fossil fuels has generated huge amounts of gaseous pollutants, namely,CO2,NOx, and countless volatile organic compounds (VOCs), among others, which urge capture and reuse whenever possible. In many industrial processes, emission of harmful gases and vapors are common, which require their removal for personnel protection and odor control. This part of overview includes a brief discussion on the fundamentals of gases and vapors' adsorption. During the past decades, tens of thousands of porous solids have been prepared and evaluated as absorbents. To rationalize that huge volume of information, the available data are critically reviewed according to the nature of the guest–host interactions that determine the adsorption forces and the related adsorption heats. Carbon dioxide can be captured and stored by clathrate formation, which is also briefly discussed.