Ambiguity aversion is a person’s rational attitude towards the indeterminacy of the probability that attaches to his future prospects, both favorable and unfavorable. An ambiguity-averse person increases the probability of the unfavorable prospect, which is what criminal defendants typically do when they face a jury trial. The prosecution is not ambiguity averse. Being a repeat player interested in the overall rate of convictions, it can depend upon any probability, however indeterminate it may be. The criminal process therefore is systematically affected by asymmetric ambiguity aversion, which the prosecution can exploit by forcing defendants into harsh plea bargains. Professors Segal and Stein examine this issue theoretically, empirically, and doctrinally. They demonstrate that asymmetric ambiguity aversion foils criminal justice and propose a law reform that will fix this problem.