This chapter focuses on the works of Karl Marx from 1845 onwards, because it is in those works that the theories and concepts for which he is best known were developed. It begins by explaining Marx’s materialist conception of history, mainly through the manuscripts published posthumously as The German Ideology (originally co-authored 1845–1846 with Friedrich Engels) and the 1859 ‘Preface’. The chapter explores some of Marx’s main concepts, including mode of production, class struggle, and ideology. The chapter then turns to Marx’s critical analysis of the capitalist mode of production, especially as found in the Communist Manifesto (1848, with Engels) and Capital Volume One (1867). Finally, it examines Marx’s views on the state and contrasts them with those of his anarchist contemporaries. While acknowledging Marx’s weaknesses, especially with respect to the analysis of race and gender, the chapter defends his continuing relevance.