Mixed oxides are the most widely used catalyst materials for industrial catalytic processes. The principal objective of this book is to describe systematically the mixed oxide catalysts, from their fundamentals through their practical applications. After describing concisely general items concerning mixed oxide and mixed oxide catalysts, two important mixed oxide catalyst materials, namely, heteropolyacids and perovskites, are taken as typical examples and discussed in detail. These two materials have several advantages: 1. They are, respectively, typical examples of salts of oxoacids and double oxide, that is, the two main categories of mixed oxides in solid state chemistry. 2. Both exhibit excellent catalytic performance in nearly crystalline state and are used in several industrial applications. 3. They have studied for many years. In addition, metal oxides functioning as a catalyst support (carrier) are included. Although the supports are very important in practical applications, and tremendous progress has been made in the past decades, few systematic reviews exist. It is notable that heteropolyacids and perovskite exhibit unique performance when used as a support. Fundamental catalytic science and technology and solid state chemistry necessary is presented for the proper understanding of mixed oxide catalysts as well as for R&D. For the latter, the concept of design of practical catalysts is very important. This is considered throughout the book. Systematically describes design principles of mixed oxide catalysts Shows how catalysis and solid-state chemistry of metal oxides are inter-related Covers all useful basic concepts of mixed oxide catalysis