This contribution is part of a PhD project studying the scope of discretionary power within the execution of sentences. Specific attention is given to the formal and substantial aspects of this discretion. The main research question refers to how the judiciary and the executive interrelate taking into consideration the constitutional principles of a state and the historical evolutions. This question will be answered by performing a comparative study involving the following countries: Belgium, France, The Netherlands, Germany and the United Kingdom. In this paper the results of the comparative study of Belgium and France will be presented. Since the 1st of February 2007, Belgian judges (meaning the multidisciplinary implementation courts) are competent to interpret and control the execution of sentences e.g. sentencing modalities regarding the nature and duration of the sentences. Before, this interpretation and control were part of the competency of theMinister of Justice (executive power) and any judicial control was absent. The reform of the Belgian sentence execution process was mainly inspired by the French model. France had already established the JAP(juge de l’application des peines) in 1958 and has thus a quite long tradition in involving the judiciary in the execution of sentences. Nevertheless the specific details in the procedure differ between the two states (e.g. multidisciplinary character, possibility for appeal…). Beside a comparison of the current interpretation of discretionary
power and the procedures, the substantive arguments as to whether or not to involve the judiciary in the execution of sentences will be examined on the basis of a literature study. Furthermore, the evolution of these debates will be discussed.