We present an overview of the academic literature on philanthropy, divided in two parts. In part one, we discuss the question of who gives how much; in part two, we discuss the question of why people give. In part one, we survey the literature on characteristics of individuals and households that are related to giving. In part two, we identify eight mechanisms as the most important forces that drive giving: (1) awareness of need; (2) solicitation; (3) costs and benefits; (4) altruism; (5) reputation; (6) psychological benefits; (7) values; (8) efficacy. We evaluate the progress in the almost 500 studies we reviewed and suggest directions for future research on philanthropy.