Intellectual disability (ID, also known as mental retardation) is a condition of arrested or incomplete development of the mind. ID is especially characterized by impairment of skills manifested during the developmental period, which contribute to the overall level of intelligence (i.e., cognitive, language, motor, and social abilities). The understanding about intellectual disability, mainly its features, causes and intervention has a long history. Researches on causes of intellectual disability lead to finding of multiple etiological factors which reflected well on its improved management techniques. The changes in terminology used describe intellectual disability also reflected our understanding about it different dimensions including social stigma. This chapter focused to give an overall view about its history, changes in terminology, classification, epidemiology, etiology, comorbidities, and management. Over the years, there are many changes and findings that have happened, yet many questions are unanswered related to this condition.