Co-occurring psychiatric conditions are extremely common among people who have autism spectrum disorder (ASD). The Oxford Handbook of Autism and Co-Occurring Psychiatric Conditions presents a compilation of the latest research in this area, summarized by internationally renowned experts. Each chapter presents an overview of the problem or disorder including information on prevalence in ASD and in the general public and a synthesis of the research on etiology, diagnostic best practices, and evidence-based intervention approaches. Case studies bring these concepts to life, and each chapter concludes with suggestions for future research directions in order to further develop our scientific and clinical understanding of the particular comorbidity. Given the fact that comorbidity is often a chronic and pervasive concern, this Handbook takes a lifespan approach, with each chapter touching on developmental aspects of the targeted problem, from early childhood through adulthood. The concluding section of the Handbook is comprised of content on clinical considerations and research approaches, including chapters on medications commonly used to treat co-occurring conditions, strategies for managing crisis situations in this clinical population, and community partnerships within an implementation science framework.