This research aims to identify the essential preconditions and critical success factors for the interaction between justice and drug treatment services, with the aim of implementing and optimising these interactions. Moreover, the research also aims to develop a guide for the actors concerned (the police and judicial authorities, the treatment sector), including the organisational preconditions for the implementation and the follow-up of projects within the framework of a ‘conditional dismissal’ (based on the principle of discretionary powers of the prosecutor).