Offender profiling is the derivation of inferences about a criminal from aspects of the crime(s) he or she has committed. For this process to move beyond deduction based on personal opinion and anecdote to an empirically based science, a number of aspects of criminal activity must be distinguished and examined. The article introduces the notion of a hierarchy of criminal differentiation to highlight the need to search for inconsistencies and variations at many levels of the hierarchy. The key distinctions are those that differentiate, within classes of crime, between offenses and between offenders. This leads to the hypothesis of a circular ordering of criminal actions, analogous to the color circle, a “radex.” The radex model, tested using Multi-Dimensional Scaling procedures, allows development of specific hypotheses about constituents of criminal differentiation: salience, models of differentiation, consistency and inference. These results support models of thematic consistency that link the dominant themes in an offender’s crimes to characteristic aspects of his or her lifestyle and offending history. Figures, references