This updated fourth edition brings together the latest knowledge and evidence base across the wide range of psychiatric and behavioural disorders presenting in people with an intellectual disability. Featuring chapters contributed by international experts, researchers, and academics from a broad range of disciplines, the book reflects current knowledge and best practice in the field, with a particular focus on contemporary approaches to clinical assessment and treatment. This edition introduces new and expanded coverage of key advances in psychiatry, including neurodevelopmental disorders such as autism spectrum disorder and ADHD, developments in neuroscience, genetics, and biomarkers, and a strengthened emphasis on service user and family involvement and co-production to inform service delivery. An essential hands-on reference book for psychiatrists and the wider group of professionals working across mental health and intellectual disability services. Also, an excellent resource for graduates, doctoral students, researchers and academics studying the range of neurodevelopmental disorders.