This introductory guide uses common language in order to demystify mental health and illness in the lives of people with intellectual disability. The varied content contains a number of case studies illustrating common mental health problems, and explains how people with intellectual disabilities can be supported to protect their mental well-being. It provides guidance on treating a person with intellectual disability for a mental health problem, adaptations to treatment that may have to be made, and how best to find the right services for an individual with intellectual disabilities and mental health problems.