This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book describes the scholarly investigation of the history of Holocaust denial as one of the principal emanations of denialism even in the 21st century. It traces the development of the phenomenon from the very days of the Second World War to the age of Web 2.0 and offers reflections on the evolution of the movement, but also on trends and methodologies that may have been apparent even in its early stages but which carry significance even to this day. The book explains the denial of genocide and crimes of mass violence in various parts of the world. It analyses options at the disposal of individual States and the international community to address the relevant conduct. The book explores key features of national and supranational strategies, but it also reflects on other, especially educational, initiatives and examines the efficiency of the relevant alternatives.