A research overview focuses on the theory that criminals show limited rationality and differences in thought processes between experienced and novice criminals. The paper describes a Chicago research study in which graduate student interviewers accompanied shoplifters -- 20 male and 14 female volunteers -- on a shopping trip. Subjects carried a microcassette tape recorder concealed in his or her clothing and were told to "think aloud." The interviewer recorded store characteristics such as security devices, layout, and number of sales clerks. Experts made proportionately more perceptual statements than did novices, whereas novices had a greater proportion of motivational statements. Unlike novices, experts tended to think in a hierarchical fashion and discuss strategies. Experts considered item inaccessibility and security devices as primary deterrents, but novices paid less attention to these factors and thought more about the risk of being caught. Usually one deterrent was enough to stop novices, but experts weighed the pros and cons more thoroughly. The implications of these results for deterrence strategies and future research are discussed. Tables and over 40 references.