Chapter contribution from John B Goodenough, Nobel Laureate in Chemistry 2019.This book provides a unique look at the chemistry and properties of complex metal oxides from the perspectives of some of the most active researchers on this class of materials. Applications of complex oxide materials are highly varied. Topics reviewed in this volume include solid-state battery research, the chemistry of transparent conductors, ternary uranium oxides, magnetic perovskites, non-linear optical materials, complex molybdenum-vanadium bronzes and other complex materials used in selective oxidation catalysis. It is written to serve as an introduction to the subject for and those beginning to work on these materials, particularly new graduate students.