Several alterations of brain function cause common mental problems in young people. ADHD, autism, tic disorders, learning difficulties, intellectual disability, and the psychotic disorders of young people are conventionally classified and described as discrete neuropsychiatric problems. Research, however, has made it clear that they are complex, variable, dimensional, overlapping, and that they frequently coexist and share aetiological influences. explores how clinicians often find themselves confronted with complex problems of diagnosis and treatment. Existing texts and guidelines, however, continue to be organized around simple conceptualization of illness categories. The book provides unified accounts of the complex psychiatric, psychological, neurological, medical, social, and educational issues that are relevant to clinical understanding.