Regardless of culture, most adult humans report experiencing similar feelings such as anger, fear, humor, and joy. Such subjective emotional states, however, are not universal. Members of some cultures deny experiencing specific emo- tions such as fear or grief. Moreover, within any culture, individuals differ widely in their self-reports of both the variety and intensity of their emotions. Some people report a vivid tapestry of positive and negative emotional experi- ences. Other people report that a single emotion such as depression or fear totally dominates their existences. Still others report flat and barren emotional lives. Over the past 100 years, scientists have proposed numerous rival explana- tions of why such large individual differences in emotions occur. Various authors have offered anthropological, biochemical, ethological, neurological, psycholog- ical, and sociological models of human emotions. Indeed, the sheer number of competing theories precludes a comprehensive review in a single volume. Ac- cordingly, only a representative sample of models are discussed in this book, and many equally important theories have been omitted. These omissions were not intended to prejudice the reader in favor of any particular conceptual frame- work. Rather, this selective coverage was intended to focus attention upon the empirical findings that contemporary theories attempt to explain.