This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book studies the worldviews and beliefs that motivate activists to advocate mass atrocity interventions. It unravels the ideological conceptions and assumptions through which anti-genocide activists view the world and humanity and make moral judgements on human suffering and violence. The book concerns the central place that anti-genocide activists allocate to the figure of the bystander in their advocacy and narratives of good and evil. It studies the views of both groups of anti-genocide activists on the principle of sovereignty, and on the related duties of the sovereign state or ruler. The book traces the ideological assumptions that make anti-genocide activists respond with horror to what they regard as the most brutal violations of that human.