In order to evaluate market institutions from a justice point of view, we need a clear concept of justice. In this chapter we investigate how justice can be defined. First, we discuss the nature of justice. Section 2 describes the theory of John Rawls and discusses some implications for the role of the government. Next, we consider the procedural justice proposed by Robert Nozick. He argues that the criterion of justice does not relate to outcomes, but only to the process that produces these outcomes. In his view, any distribution is just as long as individuals can freely choose when transacting goods on the market. Section 4 introduces the principle of meritocracy. Section 5 then presents an overview and discusses several other conceptions of distributive justice, including socialist justice and capitalist justice.