The notion of contingency plays a central role in Althusser's attempt to recast Marxist philosophy and to free the Marxist conception of history from notions such as teleology, necessity and origin. Drawing on a wealth of published and unpublished material, Stefano Pippa discusses how Althusser's unfaltering commitment to contingency should encourage us to revisit our understanding of his conceptions of structural change, ideology, politics and materialism. As grounded on contingency, Althusser's so-called 'Structural Marxism' originates in fact a 'logic of interruption' and a notion of structurally underdetermined becoming; just like his theory of ideology is radically reinterpreted on the basis of his notion of 'overinterpellation'. Though constant, Althusser's relationship with contingency has not been monolithic throughout his career. As observed by Pippa, it is possible to distinguish a 'political' and a 'philosophical' moment in Althusser's late materialism of contingency. Perhaps, as this volume suggests, the problematic coexistence of these two aspects might account for the unstable character of Althusser's late philosophical project.