The remarkable range of stoichiometries, structures, and acid-base and redox properties of the polyoxoanions of the early transition metals has lead to their use in areas as diverse as catalysis, imaging, and medicine. Recent progress in polyoxometalate chemistry has opened up the possibility of developing a nanotechnology via a bottom-up approach, starting from molecular (polyoxometalate) subunits which incorporate functionalities that are appropriate for electronic/magnetic devices, and other applications. This book provides an overview of recent progress in polyoxometalate chemistry from leading international research groups. Topics include the formation of large multi-subunit assemblies of polyoxometalates, and their functionalization, magnetic and electron-transfer properties, and biological interactions.