Dopamine is intimately linked with the modes of action of drugs of addiction. However, although its role in the initiation of drug abuse seems relatively uncomplicated, its possible involvement in the development of compulsive drug taking, and indeed vulnerability and relapse, is less clear. We first describe a modern reinforcement learning view of affective control, focusing on the roles for dopamine. We then use this as a framework to sketch various notions of the neuromodulator's possible participation in initiation and compulsion. We end with some pointers towards future theoretical developments.