"Background: A considerable amount of research has been conducted on clinical decision making (CDM) in short-term physical conditions. However, there is a lack of knowledge on CDM and its outcome in long-term illnesses, especially in care for people with severe mental illness. Thus, this project entitled ""Clinical decision making and outcome in routine care for people with severe mental illness"" (CEDAR) is proposed by participants in six European countries (Denmark, Germany, Hungary, Italy, Switzerland and UK). Methods: First, CEDAR will establish a methodology to assess CDM in people with severe mental illness. Specific instruments will be developed (and psychometric properties established) to measure CDM style, key elements of CDM in routine care, as well as CDM involvement and satisfaction from patient and therapist perspectives. Second, these instruments will be put to use in a multi-national prospective observational study (monthly assessments during a one-year observation period; N = 540). This study will investigate the immediate, short- and long-term effect of CDM on crucial dimensions of clinical outcome (symptom level, quality of life, needs) by taking into account significant variables moderating the relationship between CDM and outcome. Expected results/impact: The results of this study will make possible to delineate quality indicators of CDM, as well as to specify prime areas for further improvement. Ingredients of best practice in CDM in the routine care for people with severe mental illness will be extracted and recommendations formulated. With its explicit focus on the patient role in CDM, CEDAR will also contribute to strengthening the service user perspective. Beyond dissemination of results in scientific journals, a number of steps to ensure swift transfer of the results to routine practice are proposed. Thus, this project will substantially add to improving the practice of CDM in mental health care across Europe."