What are beliefs and what roles do they play in our behavioral and cognitive economies? Those questions are central issues not only for epistemology, but also for philosophy of language, philosophy of mind, philosophy of action, and philosophy of religion, to mention only a few fields. The authors in this volume of specially commissioned essays address them from a variety of perspectives, drawing on important classical and contemporary work on mental content, the nature of intentionality, the psychology of delusions, the role of character traits, the moral status of doxastic attitudes, and a range of other topics.