This paper aims to show that Althusser’s philosophy offers a genuine theoretical framework for thinking the finitude of practices and their relationship to alterity. Against the common image of a dogmatic thinker who tries to provide guarantees for Marxist theory and political practice, I argue that a critical thought of finitude can be found in the whole Althusserian trajectory, even in his “theoreticist” early writings, developing a theory of finitude as well as an awareness of the finitude of theory. My hypothesis is that the stakes of such a Marxist analytics of finitude are none other than the possibility for Marxism to establish, both theoretically and politically, an appropriate relationship to alterity, and the ability to revive its own emancipatory process of self-transformation.