During the 1970s, world political forces embarked on the race to breathe new life into a capitalist project of international integration. After the bankruptcy of the "heavy" keynesian-fordist model, the consensus around the adoption of neoliberal principles to facilitate the liberalization of economies reaffirms itself as a premise for the survival of this system. This facet of the process of globalization imposes the necessity, in the name of the market and an integration policy, of the adjustment the societies of the countries of both the South and the North.However, almost at the same time, already in the end of the 1970s, groups organized to protest against the rise of neoliberalism, contra the debt of underdeveloped countries, contra the precariousness of life ... in a perspective rather anti-globalization, later become alter-globalist (another world is possible). On the theoretical level, for the social sciences it is a matter of understanding the stakes of these mobilizations as well as the projects of the subjects who are engaged. Our interrogation, in fact, part of separate questions (understanding of the alter-globalization movement and a critical reading of Negri's theorization) made it possible to resume the analysis of one of the major political and social movements of the period and to pass these theorizations by the real need to understand this movement with its dynamics and its contradictions.The main idea of this thesis consists in asserting that the utopian projects of a global transformation, alter-globalization or anti-capitalist, which are more and more outlined with the reinforcement of the neoliberal globalization, especially after the most recent crisis of the world capitalism, put in check the use of the pictorial conception of the "multitude" as it has been reformulated by the negrists. This has mobilized other resources of theorists who show the contribution of Marx and its relevance to better understand our time. For the negrists we are faced with the action of the multitude of spinozist inspiration against the power of an Empire in crisis; for us, it is important to update from another perspective the marxian notion of the proletariat as expressive of a social and historical being exploited, dominated and humiliated from the diverse contributions of contemporary marxists such as Georges Lukács, Ernst Bloch, Henri Lefebvre, Pierre Naville, Jean-Marie Vincent but also Michael Löwy, Flavio Farias, Atilio Borón, to think the figures of the concrete anticipation in struggle against the institutions of global imperialism, oriented towards a new future. For this reason, this thesis work, which in fact deals with the actuality of the proletarian category-figure despite the negrist conceptualization of the image of the multitude, is divided into four major parts.With regard to the research techniques of this thesis work, a first step was devoted to the critical reading of the main authors on the concepts in question, namely the Empire versus the postmodern multitude. So are some marxist writers of the twentieth century who supported our hypothesis about the relevance actual of updating the category of the class struggle. We therefore call on the authors who have treated the proletariat category as a figure who is undergoing the oppression of global imperialism, with a view to making a categorical framework valid for a sociology of social movements.