This paper is a review of person characteristics that were present in 173 studies that were reviewed on functional assessment. The purpose was to give the reader an idea about the types of individuals for which functional assessment is appropriate and to outline persons and their characteristics which have the best research support. The majority of participants were diagnosed with intellectual disability and/or autism. Additionally more males that females were included and children were frequently studied versus adolescents and older adults. Finally, while the majority of studies employed experimental functional analysis, the number of participants per study was small. Conversely, functional analysis scales were used in far fewer studies, but with much larger sample sizes. Thus, relatively equal numbers of individuals have been studied with both methods.