Classification in Mental Retardation: Chapter 3. American Association on Mental Deficiency (AAMD), now American Association on Intellectual and Developmental Disabilities (AAIDD)
To define an intellectual disability, 42 CFR 483.102(b)(3)(i) incorporates by reference the definition in AAMD's 1983 Manual. Copies of that manual are hard to find. A scanned copy is provided below.