Intellectual disability is characterised by deficits in cognitive and adaptive abilities that initially manifest before 18 years of age. The prevalence of intellectual disability is estimated to be between 1 and 3 out of every 100 individuals in the general population. Most individuals have mild intellectual disability and the cause is generally not identified. A small percentage of individuals have severe deficits and will need lifetime supports. The diagnosis of intellectual disability requires formal psychometric testing to assess the intelligence quotient and adaptive functioning. The management of individuals who have intellectual disability is based on providing general medical care, treatment of specific behavioral symptoms, early intervention, special education, and variable degrees of community based supports. In this book we present some current issues in intellectual and developmental disability.