In a context of relevance, in the North as in the South, of the questions linked to social exclusion, I analyze the institutionalization processes of organizations of social and solidarity-based economy, that have a clear economic dimension, through a continuous activity of producing goods and services, and that pursue explicitly an aim of creating employment for disadvantaged people. I stabilize the embeddedness concept, which remains highly polysemic in the literature as well as rarely operationalized, by studying the political embeddedness of the social and solidarity-based economy organizations. It means the embedding of these organizations in the public sphere and in the public policies, according to relations of reciprocal influence. It is thus through a hypothesis of co-construction of the field that I examine the institutionalization processes of social and solidarity-based economy organizations. I analyze the twofold movement according to which, on one hand, such organizations arrive to take place in the public debate, to form a political actor and to stimulate the development of public policies. On the other hand, the specific embedding of these organizations in the public sphere and in the landscape of public policies can influence the organizational practices. Such practices are studied according to a plural conception of the organization, based on the Polanyi’s substantive definition of the economy. In order to test the heuristic value of the political embeddedness concept proposed in the dissertation, I operationalize it in two different fields, one in the North and another in the South. In such fields, the shape of the public action of the social and solidarity-based economy organizations and the shape of the State public action vary. These fields are the one of the work integration social enterprises in the Walloon region of Belgium and the one of the popular cooperatives of the state of Rio de Janeiro in Brazil. Beyond the conclusions of each in-depth case study, the research allows to ...