Open Marxism is a school of Marxism that emerged as a distinct theoretical current in the post-World War II era, developing in both Western and Eastern Europe before being consolidated by a group of theorists in the United Kingdom in the late 1980s and early 1990s. It is defined by its emphasis on the "openness" of dialectical categories, the centrality of class struggle as a dynamic and indeterminate process, the unity of theory and practice, and a strong opposition to economic determinism, positivism, and scientism within Marxist theory.

The school of thought represents a critique of and alternative to dominant forms of Marxism, particularly structural Marxism and the state ideologies of Leninism and social democracy. The term was first used in the 1950s by intellectuals like Kostas Axelos in France and later by dissident theorists in Eastern Europe, such as the Praxis school in Yugoslavia, before being adopted by a group in Britain that included Werner Bonefeld, Richard Gunn, Kosmas Psychopedis, and John Holloway. Intellectually, Open Marxism draws on a "subterranean tradition" of Marxist thought that includes Rosa Luxemburg, the early Georg Lukács, Theodor W. Adorno, and Johannes Agnoli, as well as the Italian autonomist tradition of Mario Tronti and Antonio Negri.

Open Marxism's core tenets include a critique of "closed" theories that treat social structures as fixed or governed by deterministic laws, with historical materialism being a key target. Instead, it proposes a form of analysis where social forms—such as the state, money, or capital—are understood not as static structures but as "modes of existence" of the antagonistic relationship between capital and labour. A central target of its critique is fetishism, the process by which social relations under capitalism appear as relations between things. Open Marxism argues that many "closed" forms of Marxism reproduce this fetishism in their own theories by treating social categories as objective and independent of the class struggle that constitutes them. The project has had a substantial impact, particularly in Europe and Latin America, sparking numerous debates and critiques.

The theoretical development of Open Marxism took place against the backdrop of a perceived "crisis of Marxism" that intensified throughout the 1980s. The first three volumes of Open Marxism were published between 1992 and 1995, a period that Werner Bonefeld described as one in which "the Soviet Empire had collapsed, and with great fanfare capitalism was duly celebrated as not only victorious but also as the epitome of civilisation that had now been confirmed as history’s end". This era was marked by the political ascendancy of the New Right in the West and the perceived accommodation of socialist parties to monetarism. Within intellectual circles, Marxism faced challenges from post-Marxism, which sought to announce "new times" that had supposedly rendered classical Marxist categories obsolete.

According to the editors of the foundational Open Marxism volumes, the target of these external and internal critiques was a specific variant of Marxist theory to which various kinds of "closure" applied. The Marxism that Louis Althusser had proclaimed to be in crisis in 1978 was specifically structural Marxism, a "sophisticated variety of determinism" which had previously been influential. Ironically, derivatives of structuralism, such as the Regulation Approach, flourished in the 1980s. These approaches often embraced a form of technological determinism and a teleological view of social change, particularly in their analyses of a transition from Fordism to post-Fordism. Other schools of thought, such as rational choice Marxism and critical realism, also moved away from dialectical analysis, with the latter group being described as animated by a slogan of "Back to Kant!".

Open Marxism was formulated as an "alternative reference-point" to these trends, which its proponents characterized as "closed Marxism" in a "scientistic and positivistic sense". It argued that by accepting the terms of existing reality and adopting the methods of positivist sociology, these other schools of Marxism had become blinkered. Their own crisis became a reflection of the crisis of the structures they analyzed, leading them to chase "the tail of the capitalist dog" rather than offering a revolutionary critique. Open Marxism thus sought to reassert the "dialectical dimension of Marxism", which it saw as the main casualty of these methodological shifts.

The term "Open Marxism" has a complex history and has been used to denote several distinct but related theoretical projects since the 1950s. The common thread uniting these currents is an opposition to the dogmatic, closed systems of official Marxism and a commitment to understanding Marx's theory as an open-ended, critical, and revolutionary project.

The term was first coined in the 1950s by the Greek-French philosopher Kostas Axelos within the circle of the journal Arguments. For Axelos, "Open Marxism" signified a theoretical current that, in opposition to Marxism–Leninism, refused to render Marxism an "ideology of power". His project sought an "opening" of Marxist thought to a productive dialogue with other philosophical traditions, particularly the work of Martin Heidegger, to explore fundamental questions of alienation and technology. Within the same intellectual milieu, other thinkers developed a parallel stream that understood "openness" as a turn toward the libertarian and anti-statist elements of Marx's thought. The work of Maximilien Rubel on the "anarchist Marx" and of Daniel Guérin on "libertarian communism" sought to synthesise Marxism and anarchism, arguing that Marx's core project was a critique of the state and money.