This book covers a curriculum of topics for treating patients with co-occurring intellectual disabilities and mental illness, better known as dual diagnosis (DD). Though these patients represent approximately three percent of the population, they are largely underserved due to a huge gap in the literature and limited training on this topic among non-psychiatric practitioners. They are often medically fragile and have co-occurring seizure disorders and other neurologic conditions, frequently presenting to psychiatrists with behavior problems when in fact they have undiagnosed, under-diagnosed or undertreated medical conditions.  A medical professional who is not trained to spot the nuanced symptoms can therefore be unprepared to work with such patients.  They may misdiagnose, inappropriately prescribe medications, and fail to employ the best practices as a result.