This chapter discusses the conceptual foundations of the notion of social justice during the Enlightenment before surveying the volume’s achievement in historicizing twentieth-century European proposals. Social justice presupposed the invention of the “social,” in and through the insight into informal cultural and institutional ordering. And while social justice was coined earlier in the nineteenth century, the concept became unavoidable later in the century as both left liberals and Roman Catholics responded to individuals and laissez-faire, in part by innovating a new ‘social science’. This chapter concludes by speculating about the future trajectory of claims on the notion of social justice.