This research focuses on the decision making process of the Belgian Sentence Implementation Courts, considered within the series of actions that make it possible. Decisions on early release from prison are indeed constructed in long processes, in interdependence with institutional actors in the penitentiary establishments, the central administration in charge of short prison leave which serve to prepare reintegration projects, and the Sentence Implementation Court which finally validate or inform these processes by their reasoned decision. The thesis gives an account of the complexity of the collective decision, by following the passage of the law of the sentences implementation in its three organizations, the prison, the central administration and the Sentence Implementation Courts, along the working situations of the actors. The method is inductive, and the qualitative investigation is made up of semi-directive interviews, observations of actors at work, in-depth readings of files and observations of court hearings. All of these materials make it possible to follow all the agents, supports or places of the decision and to reconstitute the trajectory of the cases, by paying attention to the documents, the practices and finally to the sharing of meaning between the actors. The thesis thus aims to show that the decision is not reduced to a situation or a moment, but that it is the product of an organizational process of sharing practice and meaning, creating the routines of collective action. The multiplicity of actors are as many tests to be crossed for the cases, producing multiple judgments on the individual and allowing notably the justification of the decision. The jurisdictionalization, only partial, of sentences implementation, introduced in 2006, thus shows in practice an administrative and centralized treatment of the requests, a complex decision system, which creates additional locks without deactivating those which existed before. ; Cette recherche porte sur la prise de décision des tribunaux de ...