This chapter surveys anarchist, utopian socialist and Marxist approaches to social justice from their foundation in the 19th century to their elaboration within two influential centres of western Marxist thinking that have proved to be especially influential in the social sciences: the Frankfurt School of Critical Theory and the spatialisation of Marxist thought in the work of David Harvey (among others). As Mitchell and Ohlsson show, radical approaches to justice have been particularly important in encouraging a strong focus on the conditions of injustice. They note that these approaches cohere around the roots of injustice in the social relations of production rather than procedure or distribution. By moving from injustice, which is what ‘actually-existing’ justice looks like on the ground, to questions of just modes and relations of production, coupled with people’s fundamental right to justification, the authors argue that radical theories of justice have profound implications for the social sciences for how they reorient how we conceive of the project of justice theorising and especially the struggle for justice.