 Louis Pierre Althusser (1918–1990) was one of the most influential Marxist philosophers of the 20th Century. As they seemed to offer a renewal of Marxist thought as well as to render Marxism philosophically respectable, the claims he advanced in the 1960s about Marxist philosophy were discussed and debated worldwide. Due to apparent reversals in his theoretical positions, to the ill-fated facts of his life, and to the historical fortunes of Marxism in the late twentieth century, this intense interest in Althusser’s reading of Marx did not survive the 1970s. Despite the comparative indifference shown to his work as a whole after these events, the theory of ideology Althusser developed within it has been broadly deployed in the social sciences and humanities and has provided a foundation for much “post-Marxist” philosophy. In addition, aspects of Althusser’s project have served as inspiration for Analytic Marxism as well as for Critical Realism and Discourse Analysis. Though this influence is not always explicit, Althusser’s work and that of his students continues to inform the research programs of literary studies, political philosophy, history, economics, and sociology. At present, Althusser’s philosophy as a whole is undergoing a critical reevaluation by scholars who have benefited from the anthologization of previously unpublished texts. His concepts are also being increasingly employed by philosophers, political theorists, and activists who have returned to Marx and to Marxian analyses in order to explain and to envision alternatives to our present socio-economic conjuncture.