Transition metal complexes as catalysts play an indispensable role in transformation of chemical substances to value-added products using less energy-consuming processes and with high selectivity and efficiency. In collaboration with the Japan Society of Coordination Chemistry (JSCC), the work is a translation of the original Japanese book focusing on metal complex catalysts that are effective in redox reactions and covers important reactions involving metal complex catalysts. It describes not only what reactions proceed, but also the intermediates they pass through and how the reactions proceed, including computational chemistry approaches. It allows you to gain a deeper understanding of the reaction mechanisms of metal complex catalysts. The scope of this book includes oxidative reactions performed by high-valent metal-oxo species, reductive reactions, bond activation and bond formation, and photocatalytic reactions. Topics in this book will be interest to those studying catalytic chemistry and related fields including coordination chemistry, organometallic chemistry, organic chemistry, bioinorganic chemistry and industrial chemistry.