This thesis aims to critically examine the relationship between post-socialism and post-Marxism, between a historical context opened by the collapse of 'really existing' socialist states in Eastern Europe, and a theoretical shift fashioned upon the idea of the immanent demise and overcoming of Marxist theory. The thesis is split into two parts. In the first part, my aim is to trace, through a detailed assessment of the writings of Antonio Gramsci and Louis Althusser - and also via the examination of the relationship between the two thinkers - a specific development of the problem of the 'superstructures' in Marxist theory, of questions of politics, the State and ideology. If Gramsci, in his conceptualisation of the politics of hegemony, and in his attempt to reformulate Marxism as a 'philosophy of praxis', pushes the issues of the theoretical and practical autonomy of revolutionary politics to the very limits of Marxism, then Althusser represents a further radicalisation of Gramsci. Arguing against a post-Marxist call for a 'return from Althusser back to Gramsci', and especially against the attempt, such as can be found with Laclau and Mouffe, to reinterpret the Gramscian problematic through a revalorisation of the fundamental concepts of the liberal-democratic tradition, I argue for a need to reassess the singularity of Althusser's philosophical contributions to Marxism, and for their importance for a contemporary reinvigoration of Marxism. In this sense, I place particular stress on two moments in the theoretical apparatus of Althusser: a) his conception of philosophy as an act, or an intervention - which seems as a powerful solution to the question of 'practicality of thought', to the injunction to 'change the world' philosophically, without a reduction of philosophy to a simple servant of political practice and its immediate ideological objectives; and b) his theorisation of politics, or, more exactly, of the specificity of revolutionary politics, which Althusser is at pains to extract and separate from the 'autonomy of the political', that is, to render heterogeneous to the general, 'autonomous', sphere of the Law, of the State and of ideology. With Althusser, the true question of the autonomy of politics can only come via a radical negation of the 'autonomy of the political', and, at the same time, through an affirmation of an irreducible singular dimension of political practice. In the second part of the thesis, I focus more concretely on the historical context of post-socialism, whilst drawing from the field of theoretical problems opened by the previous discussions of Althusser, Gramsci and post-Marxism. In this, I attempt to demonstrate that a certain rethinking and revitalisation of Marxism, and namely, of Althusser's contributions, seems as a necessary part of a critical confrontation with the post-socialist political, ideological and socio-economic realities. In the three analyses of the second part, I focus on some of the symptomatic moments of what I call the post-socialist political reason: a) the precise historical role of post-Marxist theory in the genesis of post-socialist reality, which I read via an examination of the political significance of Laclau and Mouffe's notion of hegemony in the context of the Slovenian Spring of the late 1980s; b) the relationship between liberal-democracy and nationalism, and in this, the specific structural dialectic of violence internal to the liberal State as a historical form, which I read against the paradoxes of 'democratisation' in the context of the break-up of Yugoslavia; and c) the effects of the fetishism of legal categories and of the general tendency to reduce politics to Law in the post-socialist ideological spectrum, which I contrast to the singularity of the revolutionary politics of Yugoslavia