To understand world politics, we must keep in mind both decentralization and institutionalization. Each perspective incorporates a set of distinctive questions and assumptions about the basic units and forces in world politics. International institutions are important for states' actions in part because they affect the incentives facing states, even if those states' fundamental interests are defined autonomously. Labels play a large role in contemporary writing on international relations: Appellations such as "realist," "neorealist," "mercantilist," or "liberal" pervade the literature. Liberalism is sometimes identified as a belief in the superiority of markets to state regulation of an economy. Neoliberal institutionalism also insists on the significance of international regimes and the importance of the continued exploration of the conditions under which they emerge and persist. This chapter also presents an overview of the key concepts discussed in this book.