In his liberal theory of justice, John Rawls stipulates that the principles of justice selected will be generally complied with. This assumption of full compliance is characteristic of what Rawls calls “ideal theory,” i.e., a theory that seeks to formulate and justify ideal principles of justice. David Schmidtz contends that the full compliance assumption undermines the practical relevance of ideal theory. I argue that Schmidtz’s criticisms of full compliance do not succeed. Understanding why his arguments fail requires an examination of both Schmidtz’s and Rawls’s views of the nature of justice and the function of political philosophy. I explain why full compliance can plausibly be assumed in Rawls’s ideal theory given the conception of justice he employs, and articulate the problem Schmidtz’s argument faces if it relies on his view of the role of political philosophy.