This book focuses on piezoelectric toughening, where a part of the mechanical energy inducing crack extension is converted into electrical energy or dissipated by domain alignment/domain wall movement. The effectiveness of this toughening mechanism, like other established mechanisms, depends on several aspects such as energetics of the piezoelectric transition, processing/densification of the matrix phase, particle size and distribution of secondary phase, interface between secondary and matrix phase etc. Therefore, to develop a comprehensive understanding, knowledge of all the aspects is a prerequisite. This book is therefore dedicated to all aspects of toughening by piezoelectric secondary phases.