This chapter examines the different theories and approaches that characterize the study of international relations, along with their application to the Middle East. International relations theory takes many forms and presents a variety of challenges that can be addressed using Middle Eastern cases. The field of international relations is dominated by structural realist theory. The chapter considers the assumptions of structural realism, neoliberal institutionalism, the English School, historical sociology, international society, constructivism, and relational contracting, along with post-structuralism and post-modernism. It also discusses political culture and statistical studies of world politics. In particular, it analyses some key findings from quantitative research in international relations. The chapter concludes with an assessment of power transition theory and power cycle theory, along with conceptual contributions from regional specialists.