Hospital ﬁnancing systems determine ma jor decisions made by physicians and managers within hospitals. This paper examines the impact of the transition toward an activity-based reimburse- ment system that has emerged in most OCDE countries. We consider two initial situations, one for a private for-proﬁt sector where both hospitals and physicians are paid on a fee-for-service basis and the other for a public sector under prospective budget and salaried physicians. For the private sector, our model focuses on the type of interaction (simultaneous, sequential or joint decision-making games) that should emerge between agents after the introduction of the activity-based ﬁnancing system. In the public sector, the elasticity of the demand to the level of inputs seems to play a more crucial role in the transition.