Abstract: It is natural to suppose that a prosecutor’s conviction rate– the ratio of convictions to cases prosecuted– is a sign of his competence. Prosecutors, however, choose which cases to prosecute. If they prosecute only the strongest cases, they will have high conviction rates. Any system which pays attention to conviction rates, as opposed to the number of convictions, is liable to abuse. As a prosecutor’s budget increases, he allocates it between prosecuting more cases and putting more effort into existing cases. Either can be socially desirable, depending on particular circumstances. We model the trade-offs theoretically in two models, one of a benevolent social planner and one of a prosecutor who values not just the number of convictions but the conviction rate and unrelated personal goals. We apply the model to U.S. data drawn from county-level crime statistics and a survey of all state prosecutors by district. Conviction rates do have a small negative correlation with prosecutorial budgets, but conditioning on other variables in regression analysis, higher budgets are associated both with more prosecutions and higher conviction rates.