Intellectual and developmental disabilities may affect an individual’s learning, language, social, and behavioral development. Intellectual disabilities affect an individual’s cognitive and adaptive functioning (i.e., the use of everyday practical skills required for independence), whereas developmental disabilities cover a slightly broader range of possible impairments. A developmental disability may include difficulties that limit functioning in the physical, cognitive, behavioral, or social developmental domains, and often affect more than one domain. Both intellectual and developmental disabilities first occur before the age of 18 years and vary in their impact on an individual’s functioning and achievement throughout his or her lifetime. This entry examines causes of intellectual and developmental disabilities and how screening, early intervention efforts, and early learning opportunities can help prevent some of these disabilities.