All microporous materials exhibit some level of flexibility, where their atomistic structure is affected by the adsorption of guest molecules, which can lead to expansion or contraction of the structure depending on the nature of the host-guest interactions and loading. Because of the weaker nature of the interactions in some framework materials, including MOFs, their structural response is larger in scale, whereas for inorganic nanoporous materials such as zeolites, the adsorption strain is typically in the 10 -4 to 10 -3 range. The number of known flexible MOFs has largely increased since the seminal discovery of these "soft porous crystals", and the tools available for the characterization of adsorption-induced deformation have grown significantly.