Highly dispersed nanoscale particles in polymer matrices are currently attracting great interest in many fields of chemistry, physics, and materials science. This book presents and analyzes the essential data on nanoscale metal clusters dispersed in, or chemically bonded with polymers. Special attention is paid to the in situ synthesis of the nanocomposites, their chemical interactions, and the size and distribution of the particles in the polymer matrix. Numerous novel nanocomposites are described with regard to their mechanical, electrophysical, optical, magnetic, catalytic, and biological properties. Their applications, present and future, are outlined. The book is addressed both to researchers who actively use these materials and to students entering this multidisciplinary field.