Interest, the momentary emotional feeling of curiosity, has always been a problem for mainstream psychologists because although simple interest and idle curiosity are always available to be cited as motives, they seem to be far too simple to account adequately for any aspect of human motivation or behaviour. The existence of interests, the enduring hobbies and avocations that give colour and frivolity to motivational life, gives rise to the question of why we are interested in some things rather than in others. Although this question is very important and basic to an understanding of human motivation and behaviour, it has generally been ignored or treated as simply too difficult to quantify. If properly understood, interest and interests could provide insights into many different issues, such as how transient emotional experience consolidates into lasting motives and how psychological states develop into traits. Understanding interest and interests and connecting the disparate areas within the psychology of interest are the primary goals of this book. As the first book on interest in decades, it will serve as the primary resource for anyone studying the psychology of interest.