This chapter analyses the idea of justice in light of its central place in natural law. As a specific principle of law, justice is concerned with the outer limits and harmonization of conflicting desires, claims, and interests in the social coexistence of a plurality of individuals. Taking the view that all legal problems are problems of distribution, the postulate of justice amounts to a demand for equality in the distribution or allotment of advantages or burdens. Through examples of competing formulations of the idea of justice, it is demonstrated that such formulations comprise two elements: the formal demand for equality as such; and a substantive criterion in order to determine the class to which the norm of equality is to be applied. The formal ideal of equality as such refers only to the correct application of a general rule, whereas the presupposed substantive criterion is what gives content and force to the actually efficacious formula for justice. On this background, it is argued that once the substantive criterion has been determined, it is meaningful to speak of (formal) justice. However, it is meaningless to speak of (substantive) justice in the sense of claiming that certain substantive criteria are just as opposed to others. Whereas justice, as a norm for the legislator (as a yardstick for the ‘correctness’ of the law), is merely a chimera, justice as a norm for the judge is, on the contrary, a living and palpable reality.