There is no simple or universally agreed definition of mental illness, and a wide range of conditions and disorders can be included under this term. In the National Mental Health Plan 2003-2008, mental illness is defined as "a clinically diagnosable disorder that significantly interferes with an individual's cognitive, emotional or social abilities. A diagnosis of mental illness is generally made according to the classification systems of the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-IVR) (APA 1994) or the International Classification of Diseases, Tenth Edition (ICD-10) (WHO 1992). These classification systems apply to a wide range of mental disorders (for the DSM-IV) and mental and physical disorders (for the ICD-10)." (p5).

In the context of this paper, a more narrow view of mental illness is adopted, with mental illness comprising psychotic and major mood disorders: primarily psychosis, schizophrenia, bipolar affective disorder, major depression, anxiety disorders and eating disorders. Imposing these boundaries around the definition of mental illness was necessary to contain the scope to be more manageable. These particular disorders were selected as the primary focus because they are of major concern to consumers and their families and carers as they seriously impact on current and future wellbeing. They also tend to be the mental illnesses that have received the most attention in the literature and are the core business of many specialist mental health services. Nevertheless, it is expected that the issues covered in the paper will be relevant more generally to other mental illness and mental health problems, as well as other long-term health conditions.