Abstract: The burden of proof is a central feature of adjudication, and analogues exist in many
other settings. It constitutes an important but largely unappreciated policy instrument that
interacts with the level of enforcement effort and magnitude of sanctions in controlling harmful
activity. Models are examined in which the prospect of sanctions affects not only harmful acts
but also benign ones, on account of the prospect of mistaken application of sanctions.
Accordingly, determination of the optimal strength of the burden of proof, as well as optimal
enforcement effort and sanctions, involves trading off deterrence and the chilling of desirable
behavior, the latter being absent in previous work. The character of the optimum differs
markedly from prior results and from conventional understandings of proof burdens, which can
be understood as involving Bayesian posterior probabilities. Additionally, there are important
divergences across models in which enforcement involves monitoring (posting officials to be on
the lookout for harmful acts), investigation (inquiry triggered by the costless observation of
particular harmful acts), and auditing (scrutiny of a random selection of acts). A number of
extensions are analyzed, in one instance nullifying key results in prior work.