This important collection of classic articles and papers presents a variety of perspectives on key topics in international security and conflict. These include how the structure of the international system constrains nations’ choices, how domestic politics may affect decisions on war and peace, how individual and small group behaviour can affect foreign policy, and how international organizations can affect the security of states and peoples. Some of the selections are classics, but most represent recent research and analysis. They draw on international scholars working from different kinds of theories (realist, liberal-institutionalist and constructivist) and research methods to ask why nation-states may fight violently or stay at peace.