 Socialism is a rich tradition of political thought and practice, the history of which contains a vast number of views and theories, often differing in many of their conceptual, empirical, and normative commitments. In his 1924 Dictionary of Socialism, Angelo Rappoport canvassed no fewer than forty definitions of socialism, telling his readers in the book’s preface that “there are many mansions in the House of Socialism” (Rappoport 1924: v, 34–41). To take even a relatively restricted subset of socialist thought, Leszek Kołakowski could fill over 1,300 pages in his magisterial survey of Main Currents of Marxism (Kołakowski 1978 [2008]). Our aim is of necessity more modest. In what follows, we are concerned to present the main features of socialism, both as a critique of capitalism, and as a proposal for its replacement. Our focus is predominantly on literature written within a philosophical idiom, focusing in particular on philosophical writing on socialism produced during the past forty-or-so years. Furthermore, our discussion concentrates on the normative contrast between socialism and capitalism as economic systems. Both socialism and capitalism grant workers legal control of their labor power, but socialism, unlike capitalism, requires that the bulk of the means of production workers use to yield goods and services be under the effective control of workers themselves, rather than in the hands of the members of a different, capitalist class under whose direction they must toil. As we will explain below, this contrast has been articulated further in different ways, and socialists have not only made distinctive claims regarding economic organization but also regarding the processes of transformation fulfilling them and the principles and ideals orienting their justification (including, as we will see, certain understandings of freedom, equality, solidarity, and  democracy).[1]