Although persons addicted to drugs reliably report experiencing cravings or urges during drug cue exposure, less is known about factors that may moderate this effect. This article reviews cue exposure studies with people who smoke, are dependent on alcohol, or are addicted to cocaine or opiates. Perceived drug use opportunity is found to affect urge ratings. Specifically, people who are addicted to substances and who perceive an opportunity to consume their drug of choice report higher urges than do those who do not anticipate being able to use the drug. This factor was proposed to explain why those in treatment for substance dependence report urges that are about half the strength of those in nontreatment settings. The impact of perceived drug use opportunity on urge is considered from a variety of perspectives, including conditioning theories, a cognitive appraisal framework, and motivated reasoning theory. Conceptual and methodological implications of perceived drug use opportunity are addressed.