This paper presents a theory of prosocial behavior that combines heterogeneity in individual altruism and greed with concerns for social reputation or self-respect. It shows how extrinsic incentives can crowd out intrinsic motivation, and how social norms and reputational concerns influence prosocial behavior. The authors analyze the choice by public and private sponsors of incentive levels, their degree of confidentiality and the publicity given to agents' behavior. They show that sponsor competition can reduce social welfare. The paper discusses the overjustification effect, where rewards or punishments can reduce the true motive for good deeds, leading to a partial or net crowding out of prosocial behavior. It also identifies settings where disclosing generosity may backfire. The authors analyze the choice by sponsors of incentive levels, their degree of confidentiality and the publicity given to agents' behavior. They show that sponsor competition can reduce social welfare. The paper also discusses the role of social reputation and self-respect in prosocial behavior. It shows how people engage in activities that are costly to themselves and mostly benefit others, such as volunteering, helping strangers, voting, giving to political or charitable organizations, donating blood, joining rescue squads, and sometimes sacrificing their life for strangers. The authors show that these behaviors are often motivated by social reputation or self-respect, and that rewards or punishments can affect the true motive for good deeds. The paper also discusses the role of social norms in prosocial behavior. It shows how social norms can influence behavior, and how the presence of social norms can lead to multiple equilibria. The authors show that the inferences that can be drawn from a person’s actions depend on what others choose to do, creating powerful spillovers that allow multiple norms of behavior to emerge as equilibria. The paper also discusses the role of incentives in prosocial behavior. It shows how incentives can affect the supply of prosocial behavior, and how the effectiveness of incentives depends on the informational environment. The authors show that the presence of social norms can lead to a standard upward-sloping response to incentives, but that the presence of reputational concerns can lead to a downward-sloping response. The authors also show that the socially optimal incentive scheme subtracts from the standard Pigouvian subsidy for public goods provision a "tax" on reputation-seeking, which, per se, is socially wasteful. In the market for prosocial contributions, a form of holier-than-thou competition can also lead sponsors to offer agents opportunities for reputationally motivated sacrifices that will again reduce social welfare, without any increase in the supply of public goods.This paper presents a theory of prosocial behavior that combines heterogeneity in individual altruism and greed with concerns for social reputation or self-respect. It shows how extrinsic incentives can crowd out intrinsic motivation, and how social norms and reputational concerns influence prosocial behavior. The authors analyze the choice by public and private sponsors of incentive levels, their degree of confidentiality and the publicity given to agents' behavior. They show that sponsor competition can reduce social welfare. The paper discusses the overjustification effect, where rewards or punishments can reduce the true motive for good deeds, leading to a partial or net crowding out of prosocial behavior. It also identifies settings where disclosing generosity may backfire. The authors analyze the choice by sponsors of incentive levels, their degree of confidentiality and the publicity given to agents' behavior. They show that sponsor competition can reduce social welfare. The paper also discusses the role of social reputation and self-respect in prosocial behavior. It shows how people engage in activities that are costly to themselves and mostly benefit others, such as volunteering, helping strangers, voting, giving to political or charitable organizations, donating blood, joining rescue squads, and sometimes sacrificing their life for strangers. The authors show that these behaviors are often motivated by social reputation or self-respect, and that rewards or punishments can affect the true motive for good deeds. The paper also discusses the role of social norms in prosocial behavior. It shows how social norms can influence behavior, and how the presence of social norms can lead to multiple equilibria. The authors show that the inferences that can be drawn from a person’s actions depend on what others choose to do, creating powerful spillovers that allow multiple norms of behavior to emerge as equilibria. The paper also discusses the role of incentives in prosocial behavior. It shows how incentives can affect the supply of prosocial behavior, and how the effectiveness of incentives depends on the informational environment. The authors show that the presence of social norms can lead to a standard upward-sloping response to incentives, but that the presence of reputational concerns can lead to a downward-sloping response. The authors also show that the socially optimal incentive scheme subtracts from the standard Pigouvian subsidy for public goods provision a "tax" on reputation-seeking, which, per se, is socially wasteful. In the market for prosocial contributions, a form of holier-than-thou competition can also lead sponsors to offer agents opportunities for reputationally motivated sacrifices that will again reduce social welfare, without any increase in the supply of public goods.