This book presents a comprehensive introduction to the unique and fundamental features of redox-active ligands, the preparation and characterization of their coordination complexes, and finally the importance of this class of molecules to biology, catalysis and materials. The book aim... s to provide a broadly accessible introduction to the particular features and opportunities unique to redox-active ligands. It begins with an introduction to the intellectual challenges posed by redox-active ligands and descriptions of the types of ligands and complexes in which ligand-centered redox activity are commonly observed. Following this, the book is divided into two sections as follows: The first section focuses on electronic structure and bonding, which has historically dominated this field and continues to be actively researched. The spectroscopic and other physical measurements that have been used to elucidate the electronic structure of these compounds are described. The interplay between synthesis, bonding models, and physical measurements has often been critical in shaping our understanding of these compounds. This interplay is illustrated by a number of case studies. The second section focuses on the use of redox-active complexes in stoichiometric and catalytic reactions. The scope of known reactions is presented, including examples from bioinorganic chemistry (both enzymes and model compounds). Where possible, the significance of the redox-active ligand is discussed, with an eye both to summarizing existing knowledge and pointing out possibilities for future research. This book explains the underpinnings of physical and theoretical techniques of redox-active ligands, providing up to date information on definitions, scope and applications for research scientists and graduate students working in organic and inorganic chemistry, organometallics and coordination chemistry.