Anger and aggression are prevalent problems among people with developmental disabilities and constitute primary reasons for them to be admitted and re-admitted to institutions. They are also a key reason for the prescribing of behaviour control and anti-psychotic medication to this client group. Stimulated by growing research in this area, mental health and criminal justice professionals have begun to see the benefits of anger assessment and cognitive-behavioural anger treatment for people with developmental disabilities. There is no prior text to guide anger treatment provision to this client group. This text presents a manual-guided cognitive-behavioural anger treatment protocol, grounded in a solid theoretical framework and empirical evidence for its efficacy in clinical practice. The assessment and treatment approach is designed to engage and motivate patients with recurrent and deep-rooted anger problems and their manifestation in serious aggressive behaviour. Accompanying the treatment protocol are a number of worksheets, handouts, and exercise sheets for clinicians and clients that can be accessed online.