This chapter discusses the different theories and approaches that characterize the study of international relations. Mainstream theories focus on the ways that states interact with one another in circumstances where no overarching authority governs their behavior — in other words, under conditions of anarchy. These theories include structural realism, neoliberal institutionalism, and the scholarship on relational contracting. An important alternative perspective — the English School — argues that, even under anarchic conditions, there is a high degree of orderliness in world affairs. Meanwhile, proponents of constructivism assert that states take shape in specific historical contexts, and that the conditions under which states coalesce and become socialized to one another play a crucial role in determining how they conceive of themselves and formulate their basic interests. Scholars of the Middle East have so far addressed only a fraction of the many theoretical debates and controversies that energize the field of international relations.