This dissertation examines when and why individuals behave prosocially and antisocially in economic environments. The first chapter uses a natural experiment to investigate how people respond simultaneously to two prosocial norms--restaurant tipping and generosity during the holiday season. The second chapter examines the interplay between strong social norms and their fragility by employing a laboratory experiment to see whether strong social norms for honest conduct cause victims of dishonesty to pay forward dishonesty to third parties. Finally, the third chapter investigates the role of shame in honest reporting by asking whether individuals are more truthful when they know their statements will be subject to ex-post disclosure. Taken together, we gain insights into the motives for altruistic and ethical behavior as well as the roles social norms play in promoting or deterring such behavior. This research both draws from and extends to existing research in psychology and organizational behavior as well as economics.