An attempt is made to identify the many different functions that assessment of an individual's repertoire can serve. Implications of these functions for the character of and evidence about assessment devices are suggested. The functions fall into two general groups, those which influence decisions regarding an individual learner, and those which influence policy, program development, and scientific knowledge. The first group of functions is presented in a rough chronological sequence such that they form a "behavioral assessment funnel," beginning with functions involving broad-band assessment to identify likely persons and skill areas, and narrowing to the precise pinpointing, monitoring, and follow-up functions. The contribution of behavior analysis and behavior therapy to assessment methodology in this sequence is identified as well as the areas where more traditionally conceived methods are still useful. The second group of functions and behavioral contributions to it are then discussed.DESCRIPTORS: behavioral assessment, functions of assessment, selection of assessment devices, traditional assessment, clinical assessment, educational assessment, phases of assessment, construction of assessment devices Applied behavior analysis has made profound contributions to the technology for assessing repertoires. At the same time, behavior analysts have often rejected or ignored valuable existing ("traditional") knowledge and technology for clinical and educational assessment (Cone, 1977;Goldfried, 1977;Hawkins, 1975;Nelson and Bowles, 1975; Hlartmann, Note 1). The purposes of the present paper are three. The first is to identify several different phases and functions in assessment. The second is to put the contributions of behavior analysis in context, showing where the contribution thus far has been greatest and where previously existing knowledge and technology can be of value