All materials possess interatomic or interionic voids that are typically too small for any molecular species to enter. However, there is a class of crystalline materials that contain internal voids, and apertures, that are large enough for molecular species to enter and pass through. These materials are termed microporous and form a highly diverse group of compounds that may be synthesised or occur as natural minerals. The composition of microporous materials ranges from being exclusively inorganic to inorganic-organic hybrids and their applications vary from 1 Mton annual usage in detergents, to hosts for superconducting carbon nan-otubes. In this contribution, new and mature aspects of the synthesis, scope, modification and application of microporous materials are covered to provide the reader with an overview of this exciting field of materials chemistry.