International institutions provide order and meaning; they structure and facilitate cooperation in world politics. This lecture is intended to introduce the main theoretical debates in international relations (IR) on international regimes and regime complexes, international organizations, and international norms. We will compare what kind of answers major IR theories, like realism, institutionalism, and constructivism - but also critical and feminist approaches -  offer on fundamental questions of the emergence, shape, and consequences of international institutions: for example, why do sovereign nation states delegate authority to international institutions? How do international regimes like the Climate regime facilitate compliance? When do states leave international organizations? What explains the diffusion of international norms, such as gender equality and sustainable development? While some empirical examples will be included for illustrative purposes, the lecture is theory-oriented and  intended to give students a solid foundation in the study of international institutions. At the end of this lecture course students should be able to give nuanced assessments of differing theoretical approaches in relation to their research goals and application to IR.