Marx's sociology is reinterpreted as a form of realist social theory in this book which extends Roy Bhaskar's philosophical realism into the social sciences. The book puts forward an anti-reductive ontology of society, identifying a stratified social world in which individuals, practices and structures are the key levels. Within this framework the key task of realist social theory is to investigate the dialectical interplay between these key levels in shaping historical processes and systemic outcomes. By constructing historical materialism as realist social theory it becomes possible to resolve many long standing dilemmas in Marxist discourse, such as voluntarism versus determinism, humanism versus economism and agency versus structure. Social realism provides the means to theorise the interface between subject and system and/or individual and society which reveals the emergent nature of social systems. The book also argues that realism requires a thorough materialistic application in order to avoid the residual idealism or empiricist pluralism in social analysis of postmoderism or neo-Weberian analysis, both of which are contested here.