Expands Barker's theory of behavior settings by proposing an additional method o f classifying settings based on their functional~behavioral aspects-the setting phenotype. Although behavior setting theory has been widely hailed as a revolutionary contribution to behavioral science, it has had limited impact on general psychology. This may be due in part to a reliance on a purely structural method o f classifying behavior settings-the setting genotype. Behavioral data were collected f r o m 510 meetings o f 13 self-help groups from a mutual help organization for persons with problems in lying. A cluster analysis was performed to uncover meaningful behavioral patterns among the groups. Four phenotypes were identified: personal, impersonal, small talk, and advising. Mutual help group phenotype was f o u n d to be related to a set o f setting characteristics as well as to overall rated change o f group members. The results are discussed in light of the significance o f the phenotype construct for making behavior setting theory more relevant for social scientists.The legacy of the p e r s o n -e n v i r o n m e n t debate is an appreciation by social scientists of the i m p o r t a n c e of both person and place in u n d e r s t a n d i n g h u m a n behavior (Bandura, 1978; Bern & F u n d e r , 1978;Pervin, 1987).'Support for this research came from an NIMH grant (MH37390) awarded to Julian Rappaport and Edward Seidman. We thank Brian Luke, the associate editors, and three anonymous reviewers for comments on an earlier draft; also Julie Genz, Thomas Reischl, Linda Roberts, and the members of the GROW organization for making this study possible. 2All correspondence should be sent to Douglas Luke,