Atomically dispersed metal cations and small polyatomic cationic structures co-ordinated to the surface of porous matrices exhibit different properties from the same cationic species contained in a bulk oxide or supported on amorphous carriers. This subject is treated to an extensive review, showing how an understanding of it is essential to the development of a new generation of solid catalysts. There are also opportunities to shape the catalytic properties of the transition metal cations in microporous and mesoporous matrices. The book covers both theoretical and experimental aspects, including the distribution of framework Al atoms in Si-rich zeolites, distribution and siting of charge-exchanged metal cations, electronic, adsorptive and catalytic properties of metal cations, and correlation of metal cation structure and siting with catalytic activity.