Social justice is a crucial ideal in contemporary political thought. Yet the concept of social justice is a recent addition to our political vocabulary, and comparatively little is known about its introduction into political debate or its early theoretical trajectory. Some important research has begun to address this issue, adding a valuable historical perspective to present-day controversies about the concept. This article uses this literature to examine two questions. First, how does the modern idea of social justice differ from previous conceptualisations of justice? Second, why and when did social justice first emerge into political discourse?