The introduction of coordination complexes into (micro/meso)porous materials to benefit from confinement effects in catalysis was initiated about fifty years ago. The approach clearly draws its origin from a parallelism with enzymatic catalysis, where the active site and its microenvironment act in concert to direct the selectivity of chemical reactions. Today, many methodologies for the synthesis of confined complexes are available to the chemist, and the fine characterization of these materials requires the combination of several experimental techniques and modeling tools. The confinement effect generally results from the combination of several effects at long and short distances from the active center, which can affect the transport phenomena as well as the concentrations or the pressure, the adsorption/desorption stages, or the very nature of the transition states. The deconvolution of these different effects is a real challenge in chemistry, and molecular simulation plays an invaluable role in the future of confined catalysis.