The concept of passion is one we regularly use to describe our interests, and yet there is no broad theory that can explain the development and consequences of passion for activities across people's lives. In The Psychology of Passion, Robert J. Vallerand presents the first such theory, providing a complete presentation of the Dualistic Model of Passion and the empirical evidence that supports it. Vallerand conceives of two types of passion: harmonious passion, which remains under the person's control, and obsessive passion, which controls the person. While the first typically leads to adaptive behaviors, the obsessive form of passion leads to less adaptive and, at times, maladaptive behaviors. Vallerand highlights the effects of these two types of passion on a number of psychological phenomena, such as cognition, emotions, performance, relationships, aggression, and violence. He also discusses the development of passion and reviews a range of literature on passion for activities.