The French intellectual Georges Bataille (1897–1962) developed base materialism in his work during the late 1920s and early 1930s as an attempt to break with all existing materialism. This essay is an explication of base materialism and its radical implications for contemporary theory. Bataille argues for the concept of an active base matter that disrupts the opposition of high and low and destabilises all foundations. Then he attempts to use this to develop a radical libertarian Marxism, opposed to both Stalinism and fascism. Although it provided a critique of the emphasis in Marxism on production, the active flux of base matter could not be contained in a political discourse. This means that Bataille's thought has an impact beyond the political and into the wider domain of theory. One example of this is the influence of base materialism on Derrida's deconstruction, and both share the attempt to destabilise philosophical oppositions by means of an unstable ‘third term’. This explains why Bataille's materialism does not appear as conventionally materialist, and why it has had little impact within contemporary materialism. Despite attempts to force base materialism into the mold of a new form of materialism it disrupts conventional materialism and the ‘radical’ politics that often goes with it. Bataille destroys the promise of liberated spaces and offers a more radical and disorienting freedom which inscribes instability into all discourses. It is this that defines the importance and necessity of Bataille's base materialism today.