In order to understand the complex behavior of an individual, what that individual has learned must be understood. Unfortunately, behavior analysis and psychology in general have not studied the cumulative effects of the learning principles. However, there are concepts in behavior analysis that, although not well researched, address this area. These concepts are basic behavioral repertoires, cumulative hierarchical learning, behavioral cusps, generative instruction, and pivotal areas of functioning. The importance of these concepts for assessment, the selection of target behaviors, and curriculum design is described.