Imagine you receive a letter. It is from the Department of Health. In the letter you are asked to send it back with an answer indicating whether or not you want to become an organ donor. You decide to deal with it later. Three weeks later, you meet up with some friends. At one point the discussion turns to organ donation." Of course everyone should be an organ donor" seems to be the opinion of you and your friends. But then you suddenly remember the unreturned letter. You start to wonder." Why didn't I return the letter?" This dissertation is about attitudes, more specifically, about feelings versus thoughts in attitudes. The distinction between feelings and thoughts has been made since the Greek philosophers. At the same time it is often neglected when assessing attitudes (Eagly, Mladinic & Otto, 1994). However, your feelings and thoughts do not always coincide and could even contradict each other. For example, it could be that your thoughts about organ donation are quite favorable, while your feelings are more mixed. This could explain the discrepancy between your favorable opinion about organ donation and your behavior. As we will see in this dissertation, it is also possible that people's overall attitudes toward organ donation are favorable, but that this overall attitude deviates from their feelings. In this dissertation, I argue that the affectcognition distinction is a crucial distinction that is essential for our understanding of attitudinal processes. Identifying feelings versus thoughts in attitudes immediately raises the question of what an attitude encompasses. We could adopt the definition of attitudes proposed by Eagly and Chaiken (1993, p. 1):"