Previous economic analyses of plea bargaining have largely ignored its impact on the deterrence of crime. Instead, they have focused on the bargaining between a defendant and a prosecutor once a crime has been committed. This article remedies this deficiency by asking how the practice of plea bargaining influences the determination of criminal punishment and thereby the supply of crime by rational offenders. The key question examined is, how do the ex post objectives of prosecutors affect the ability of legislatures to implement criminal punishments aimed at achieving optimal deterrence? Various prosecutorial objectives are considered in answering this question.