This article describes research-based principles of successful treatment interventions in individuals with co-occurring disorders. These principles are placed in the context of an integrated model of service delivery that utilises a common language or treatment philosophy that makes sense from the perspective of both mental health treatment and substance disorder treatment fields.The article begins with an overview of the clinical and programmatic dilemmas faced by clinicians in treating these ‘dually diagnosed’ individuals and then enumerates 7 principles of treatment. These are:dual diagnosis is an expectation, not an exception, within any of the 4 subtypes of comorbidity (using a subtyping model based on high/low severity of each disorder);the most significant predictor of treatment success is the provision of an empathic, hopeful, continuous treatment relationship in which integrated treatment and care coordination are provided over time;within the context of this relationship, caretaking and case management are balanced with empathic detachment, empowerment and confrontation at each point in time;within this ongoing treatment context, both mental illness and substance disorder are considered primary, and integrated dual primary treatment is provided;both mental illness and addiction are examples of not just random primary disorders, but chronic biological mental illnesses which can be understood using a disease and recovery model;the model defines parallel phases of recovery, which themselves define phase-specific treatment interventions; as a result, there is no single correct intervention in this model. For each individual, the correct treatment must be matched to subtype, diagnosis, phase of treatment and extent of patient motivation and disability; andwithin a managed-care system, these interventions must be further individualised by a discrete level of care assessment for each disorder.These principles provide a template both for developing practice guidelines to determine individualised clinical treatment matching, as well as providing a template for large-scale system initiatives for the creation of comprehensive continuous integrated systems of care, and for assigning roles for each type of programme within those systems. These large systems initiatives are currently underway in several US states, and provide a laboratory for further research on this model.