This book is the first one entirely devoted to the topic of constraint debugging; it presents new approaches to debugging for the computational paradigm of constraint programming. The book is based on the European research project DiSCiPl. It consists of an introduction and three parts, each of them composed of several chapters. The introduction presents the DiSCiPl debugging methodology and explains how the technical chapters are related. The three parts on correctness debugging, performance debugging, and user cases offer a total of 13 consistenly written chapters.