Context Hospitals in European countries apply a wide range of quality improvement strategies; however, knowledge on the effectiveness of these strategies is limited. Objectives We propose to study the effectiveness of quality improvement systems in European hospitals. Specific research objectives are: a) to develop a maturity classification model for the assessment of organizational quality improvement systems in EU hospitals; b) to investigate associations between the maturity of quality improvement systems and measures of organizational culture, professional involvement and patient empowerment (at hospital level); c) to investigate associations between the maturity of quality improvement systems and measures of clinical effectiveness, patient safety and patient involvement (at patient and departmental level); d) to identify factors influencing the uptake of quality improvement activities by hospitals including external pressure as enforced by accreditation, certification or external assessment programmes. Design DUQUE will apply multi-method approaches to data collection, measurement and analysis. Data will be collected at hospital, departmental, professional and patient level. We will employ a multi-level study design in which patient-level data is nested in hospital departments, which are nested in hospitals in different EU countries. Setting We will collect data at hospital and departmental level in the Czech Republic, France, Germany, Poland, Portugal, Spain, Turkey and the United Kingdom in 30 randomly selected hospitals. In each country, for 12 of these 30 hospitals we will carry out additional data collection at the patient-level. Expected outcomes The products of DUQUE will include a catalogue of instruments to build a department and/or hospital specific quality and safety programme and an appraisal scheme to assess the maturity of the quality improvement system.