The Matrix Model is essentially a strategy for managing dual diagnosis across a range of agencies. It is a way of implementing partnership working across services and commissioning structures. The Matrix Model was born out of hard experience at the coalface of dual diagnosis treatment at a tier four service in Bristol. A very common experience, which many may recognize, was that clients with complex mental health and addiction needs were being sent from 'pillar to post' in their treatment. Things needed to change. Here is a method of how things can change. Briefly, professionals in the drug/alcohol and mental health fields co-locate, working with clients in each other's workspaces. In doing this, they create nodes of integration. These nodes of integration link through parallel-working to create a matrix. Outcome and key recommendation is that professionals in the drug/alcohol and mental health fields co-locate in each other's agencies, adopting an assertive outreach approach to working with dual diagnosis/complex-needs clients.