International and domestic law offer a study in contrasts: States' legal obligations often depend on their consent to specific international legal norms, whereas domestic law applies to individuals with or without their consent; enforcement in international law is weak and, for many international treaties, non‐existent, whereas states spend considerable resources to create centralized coercive enforcement mechanisms; and international law is characterized by much less institutional differentiation and specialization of functions than domestic legal systems are. These differences have invited a number (...) of skeptical challenges to international law, 3 of which we explore in this essay. The first points to 1 or more of the deviations of international law's institutional structure from that of a modern state's legal system as a basis for denying that international law is really “law.” Central to the debates over international law's status as law are concerns about whether and why the concepts of law inherited from domestic legal systems should serve as the blueprint for theorizing law in general and international law in particular. The second skeptical challenge targets international law's legitimacy. It claims that we lack reasons to treat international legal norms or the exercise of political power by international institutions, as anything other than an attempt by states to advance their national interests. If this challenge succeeds, states and other subjects of international law have merely prudential reasons to comply with it rather than a moral duty to obey it. Following a brief description of recent debates over how we ought to understand the concept of legitimacy when used to assess international political practices or global governance, we survey several possible bases for a moral duty to obey or respect international law. These include state consent, instrumental accounts of legitimate authority, and global democracy. The third set of challenges focuses on the relationship between state sovereignty and international law. International rules and institutions often make demands for reform affecting the domestic law of a state in order to elicit compliance with international law. Skeptics argue that the rule of international law is incompatible with states' political self‐determination. Regardless of whether their defense of this claim ultimately succeeds, thoughtful engagement with it may well require us to rethink some of the fundamental concepts and normative ideals in political philosophy, including state sovereignty, democracy, individual rights, political authority, and political obligation. (shrink)