We present an overview of theories and research on charitable giving in economics, sociology, social psychology, and marketing from the past 50 years (1955-2005). We identify seven mechanisms as the most important forces that drive giving. The seven principles of philanthropy are: (1) solicitation; (2) awareness of need; (3) costs; (4) reputation; (5) psychological benefits; (6) changing the world; (7) confidence. We discuss each of these mechanisms and show how they are related to the findings of survey and experimental studies on philanthropy, and how practitioners can use them.