A critical assessment and appreciation of Althusser's contribution to Marxism, focusing on his metaphilosophical positions, the thesis of the 'epistemological break' (and its subsequent revisions), his account(s) of the relation between Hegel and Marx, and of the materialist dialectic. It is argued that Althusser, largely, for polemical-political reasons, has camouflaged constructive and defensible positions as provocative formulations, designed to entice or outrage practitioners of the various obscurantisms (structuralism, neo-Hegelianism) that have plagued the best Marxist thought of the past several decades. Althusser's contribution to Marxism, it is maintained, is best grasped from the point of view of contemporary philosophy of science; and his distinctively philosophical practice can best be viewed as an attempt to determine what must be the case if Marx is indeed taken to have 'opened up the continent of History' for science.