"Intellectual disability" is a term used when a person has certain limitations in mental functioning and in skills such as communicating, taking care of him or herself, and social skills. These limitations will cause a child to learn and develop more slowly than a typical child. Following a brief story about a child with an intellectual disability, Matthew's Story, this fact sheet presents information on the following: (1) What is an Intellectual Disability?; (2) What Causes an Intellectual Disability?; (3) How Common are Intellectual Disabilities?; (4) What are the Signs of Intellectual Disability?; (5) How are Intellectual Disabilities Diagnosed?; (6) Definition of "Intellectual Disability" under the Individuals with Disabilities Education Act (IDEA); (7) Help for Babies and Toddlers; (8) Help for School-Aged Children; (9) Educational Considerations; (10) List of Organizations; (11) Tips for Teachers; and (12) Tips for Parents.