This book provides the reader with a unified understanding of the rapidly expanding field of molecular materials and devices: electronic structures and bonding, magnetic, electrical and photo-physical properties, and the mastering of electrons in molecular electronics. This revised edition includes updates and additions on hot topics such as molecular spintronics (the role of spin in electron transport) and molecular machines (how electrons can generate molecularmotions).Chemists will discover how to understand the relations between electronic structures and properties of molecular entities and assemblies, and to design new molecules and materials. Physicists and engineers will realize how the molecular world fits in with their need for systems flexible enough to check theories or provide original solutions to exciting new scientific and technological challenges. The non-specialist will find out how molecules behave in electronics at the most minute,sub-nanosize level.