From October 1989 until March 1991, field work was conducted in five prisons. In each institution, researchers spent 4 to 6 weeks gaining the confidence of the inmates through frequent contact and participation in work and recreation activities. Forty-three inmates convicted of commercial robberies then consented to interviews. All of them were interviewed several times at length. Where possible, information provided in the interviews was corroborated from official records. Based on the information obtained, the robbers were divided into three types: "desperation robbers," "beginners," and "professionals." "Desperation robbers" lack a significant criminal career and commit their first and often only robbery in a desperate effort to solve their financial problems. "Beginners" commit their first robbery after having been criminally active for years, a period during which the severity and the frequency of their crimes increased. "Professionals" have also been criminally active for a long time, but they have committed more robberies than the "beginners." The three types of robbers differ in the choices they made during the planning and execution of their robberies and their readiness to use violence. Desperation robbers and beginners commit their robberies without much preparation. All robbers denounce violence that exceeds what is required for the effective execution of the robbery. Desperation robbers are more likely to terminate a robbery attempt if they meet with resistance that would require them to use force. Both beginners and professionals are prepared to use violence if it is required to complete the robbery. Only desperation robbers show remorse for the suffering inflicted on their victims. By using the perspectives upon which the reasoning of robbers was based, their decisionmaking became rational, although to the nonoffender it would appear irrational and immoral. 2 tables and 10 references