Psychiatric involvement with intellectually disabled persons has a long history, one that begins in the nineteenth century, when neuropsychiatrists were frequently superintendents of the early institutions for intellectually disabled persons. Interest in intellectual disability among psychiatrists subsequently waned for several reasons. First, insight-oriented therapy became the primary form of treatment, and persons with intellectual disability were generally considered to be poor candidates for such therapy. Second, an emerging focus on normalization led to an emphasis on educational approaches and behavior modification techniques that tended to involve other professionals who minimized the importance of a diagnosis of a psychiatric disorder. Moreover, there was a public reaction to psychotropic medications being used excessively in state facilities for behavior reduction without adequate attention being given to comprehensive treatment programs. This use of psychotropic drugs led to an active effort to reduce their use and also led to increasing involvement of nonmedical professionals in the treatment of intellectual disability. However, with the emergence of improved assessment (State et al. 1997; Szymanski and King 1999), a biopsychosocial approach to treatment, and the acknowledgment that school and community placements most commonly fail because of disruptive behavior, there has been a renewed focus on psychiatric diagnosis and treatment and on better understanding how mental disorders present in intellectually disabled persons. Advances in the neurosciences, developmental psychology, developmental psychopathology, phenomenology and classification, family therapy, behavior therapy, and drug treatments have led to renewed interest in psychiatry and a commitment to better diagnosis and treatment of intellectually disabled individuals with mental illness. Recognition of the role of life experience in brain development and a better understanding of the natural history and developmental trajectory of specific behavioral phenotypes in intellectual disability syndromes also have led to greater participation of psychiatrists with other professionals in research on psychiatric disorders in persons with intellectual disability.