The principal aim of this work is to give a better understanding of the concept of reward and, at a psychological level, its role in drug dependence. The author focuses on brain mechanisms that are associated with the processing of reward and dependence, as well as the processes common to the different forms of substance dependence. The present study shows that reward is an important determinant of motivated behaviour and is also thought to play an important motivational role in the explanation of addiction. A large body of empirical evidence supports the idea that the reinforcing properties of psychoactive drugs are mediated by the meso-corticolimbic dopamine system, which is also involved in the processing of reward information in the brain. This study is part of a theoretical framework, which combines psychological and neurobiological models of motivation and dependence. It also integrates the results of neuroimaging studies and of a large questionnaire exercise.