Around 588,700 Australians (3% of the population) have an intellectual disability. Most are aged under 65 years (436,200). It is common for people with intellectual disability to have other types of disability, the most common being psychiatric disability.

Generally speaking, a person with an intellectual disability has difficulty understanding the subtleties of interpersonal interactions. They learn and process information more slowly than people without an intellectual disability. They can have difficulty communicating, managing daily living skills, and have difficulty with abstract concepts, such as money and time.

A person is said to have an intellectual disability if, before they are 18 years of age, they have both an IQ of below 70 and have significant difficulty with daily living skills, including looking after themselves, communicating and taking part in activities with others.

An intellectual disability may have been caused by problems during pregnancy and birth, health problems or illness, a genetic condition or environmental factors, brain injury or infection, exposure to toxins, substance dependence during pregnancy, or growth and nutrition problems.

Arbitrary categories of mild, moderate, severe and profound levels of intellectual disability are defined on the basis of IQ scores. These levels give some guide to the level of support someone might need, but the way the person functions in their life can also depend on other factors such as personality, their circle of support, their coping skills and other disabilities they may have.

They still experience and feel things like joy, anger, pride, hurt, jealousy and other emotions, and want the opportunity to have a range of life experiences. They learn and develop more slowly than average, but can learn to adapt to new situations and enjoy life independently with support.