This general review situates Australian research within a framework that quantifies and describes mental health needs of the population with intellectual disabilities across the life span, surveys service provision, and develops the evidence base to inform clinicians regarding assessment and management of psychopathology and psychiatric disorder in people with intellectual disabilities. In particular, Australian research has examined the prevalence, nature, associated factors, and trajectory of clinically significant psychopathology from childhood to adulthood. The Developmental Behavior Checklist and a suite of versions, including an adult version, have proven to be robust instruments in identifying and describing psychopathology in people with intellectual disabilities. Australian researchers have also examined aspects of psychiatric assessment in a population with cognitive and communication impairments, which has direct relevance to clinical practice. Surveys and audits of policy, real-life practice, and service structure and provision have identified serious deficiencies in the training of health professionals and the provision of mental health care to people of all ages with intellectual disabilities and mental ill health. In light of the weight of the evidence, state and federal governments are developing new service models and there are increasing opportunities for professional education and training.