This dissertation consists of three self-contained essays on belief formation and on the role of beliefs for prosocial behavior. The first chapter is co-authored with Peter Schwardmann and Joel van der Weele. Does the wish to convince others lead people to persuade themselves about the factual and moral superiority of their position? We investigate this question in field experiments at two international debating competitions that randomly assign persuasion goals (pro or contra a motion) to debaters. We find evidence for self-persuasion in incentivized measures of factual beliefs, attitudes, and confidence in one's position. Self-persuasion occurs before the debate and remains after the debate. Our results lend support to interactionist accounts of cognition and suggest that the desire to persuade is an important driver of opinion formation. The second chapter is co-authored with Lorenz Goette. We propose a novel experiment that prevents social learning, thus allowing us to disentangle the underlying mechanisms of social influence. Subjects observe their peer's incentives, but not their behavior. We find evidence of conformity: when individuals believe that incentives make others contribute more, they also increase their contributions. Conformity is driven by individuals who feel socially close to their peer. However, when incentives are not expected to raise their peer’s contributions, participants reduce their own contributions. Our data is consistent with an erosion of norm-adherence when prosocial behavior of the social reference is driven by extrinsic motives, and cannot be explained by incentive inequality or altruistic crowding out. These findings show scope for social influence in settings with limited observability and offer insights into the mediators of conformity. The third chapter is co-authored with Christian J. Meyer. We study incentivized voluntary contributions to charitable activities. Motivated by the market for blood donations in Germany, we consider a setting where different incentives coexist and agents can choose to donate without receiving monetary compensation. We use a model that interacts image concerns of agents with intrinsic and extrinsic incentives to donate. Laboratory results show that a collection system where compensation can be turned down can improve the efficiency of collection. Image effects and incentive effects do not crowd each other out. A significant share of donors turn down compensation. Heterogeneity in treatment effects suggests gender-specific preferences over signaling.