There is general agreement that delinquent youth are not all alike and cannot be expected to respond to a given program in the same way. To increase understanding of interactions between programs and client outcomes, a typology of clients was created based on 14 personality scales, using scores obtained at the point of program admission. The article reports on the methods used to construct the typology, the substances of the classification system and the steps taken to ensure its continued development. It also emphasizes the advantage to typology development of ongoing access to an information system that includes recidivism and other outcome data. Locating a typology in an ongoing process of data collection enhances development of the type by the opportunity to test predictions about type-program interactions. Also, as the population of delinquents changes, the typology can be revised to reflect those changes. Finally, it creates a typology that can be applied to an entire juvenile justice system. Tables, appendix, references