["Criminology & Public Policy, Volume 20, Issue 4, Page 621-643, November 2021. ", "\n\nResearch Summary\nThis study examines the independent and joint effect of ambiguity and perceived certainty of apprehension on law‐breaking decision‐making. Data come from a survey of experienced drivers (N = 1147) who viewed videos depicting a car speeding on an interstate highway under experimentally manipulated circumstances. The sampled drivers were generally ambiguity averse, opting to reduce speeding as ambiguity about the perceived certainty of apprehension increased. However, perceived ambiguity interacted with perceived certainty such that increases in ambiguity increased the deterrent effect of ambiguity for low certainty probabilities and decreased the effect for high probabilities.\n\n\nPolicy Implications\nAmbiguity may serve as a valuable tool for increasing the efficacy of crime‐prevention strategies, especially for crimes with naturally low levels of risk. However, researchers should think carefully about the effects of ambiguity when analyzing the efficacy of certainty‐based policies because the injection of ambiguity can both increase and decrease legal compliance. Also, discussed are the implications for a key function of policing—traffic safety.\n\n"]