This chapter delineates two types of ideal theory that are found in Rawls’s corpus of work. The first is ideal-method theory, which is theory constructed using idealizing assumptions that do not directly correspond with the actual world. The second is ideal-content theory, namely criteria for assessing whether something is a perfectly justice institution. The chapter provides an independent justification for both types of theory, arguing that ideal-method theory is valuable within certain parameters; for instance, the idealizing assumption of strict compliance helps to clarify the distinction between distributive and retributive justice. The chapter illuminates the value of ideal-content theory by clarifying and defending Rawls’s claim that nonideal theory depends on ideal-content theory. In particular, it argues that in order to gain a systematic grasp of the more pressing problems of nonideal theory it is plausible to argue that ideal-content theory is necessary.