This chapter deals with normative international relations theory, a field of study that relies on a variety of approaches and theories to explore moral expectations, decisions, and dilemmas in world politics. Normative IR theory has adopted—and adapted—conceptual categories such as communitarianism and cosmopolitanism from political theory. It also borrows from moral philosophy to designate different types of ethical reasoning, such as deontology and consequentialism. The chapter begins with an overview of the history, influences, and some of the categories that normative IR theory brings to the study of international relations. It then examines the ways in which normative IR theory engages with the hidden ethical assumptions of a range of IR approaches. The case study considers the ethics of war in the Iraq war.