"Mental disorders affect 38.2% of the EU population. For reducing the associated burden, countries across Europe engage in costly re-organizations of mental health care systems. Reforms focus on one controversial core question: Should systems be functional or integrated? In functional systems, separate staff in different services are in charge of in- and out-patient care (to enhance specialization). In integrated systems, the same staff are responsible across services (to strengthen co-ordination and avoid fragmentation). So far, there is no sound research evidence to inform the debate and far reaching policy decisions.Integrated and functional systems co-exist in some countries. This provides the unique chance to compare the effectiveness of the two systems independently of country specific contexts. We will conduct a large-scale comparison in countries with different traditions, levels of service provision and funding systems of mental health care (Belgium, Germany, Italy, Poland, United Kingdom).We will work as a multi-disciplinary team (psychiatrists, psychologists, nurses, sociologists, public health experts, health economists) and prospectively follow-up more than 5000 patients with major mental disorders over a 9 month period. Across countries, we will compare the effectiveness and cost-effectiveness for clinical and social outcomes (including quality of life), patients’ health and social needs, safety and quality of care of patients in the two systems. We will also establish how patients and clinicians experience the advantages and limitations of each system, and identify the policies and legislative frameworks determining practice in the two systems.We will produce guidelines for policies specifying in what context and for which patient groups (e.g. older age) functional or integrated systems are preferable, and disseminate these widely (to governments, scientific societies, professional bodies, users and carers’ organizations)."