Polyoxometalates are anionic metal-oxo nanoclusters, which constitute a unique class of compounds owing to their rich solution equilibria and their unique compositional, electronic, reactive, and structural diversity. This book reviews metal-oxide cluster chemistry by covering topics ranging from fundamental aspects (i.e., structure, properties, self-assembly processes, derivatization) to functional materials that incorporate these molecular units, as well as their applications in the fields of current socioeconomic interest, such as energy storage systems, catalysis, molecular electronics, and biomedicine. Edited by prominent researchers in the field of polymer and polyoxometalate chemistries, the book compiles contributions from some of the most distinguished and promising scientists worldwide in such a way that it will appeal to a general readership involved in research areas related to chemistry and materials science.