Delirium is a frequent and serious problem in hospitalized patients; it is associated with multiple hospital-acquired complications. There is evidence that the incidence of deliri-um may be minimized by multimodal interventions (pain management, shortening the duration of mechanical ventilation, light sedation, avoiding benzodiazepines, routine delirium monitoring, and early mobilization). Even though a clear association between sleep and delirium has not been established, many studies suggest that sleep disturban-ces may be a key risk factor for the development of delirium. Therefore, sleep promoti-on is becoming an integral part of clinical care. The project support the hypothesis that non-pharmacological preventive interventions promoting sleep (sleep protocol) positive-ly influence the quality of sleep and reduce the incidence of delirium in hospitalized patients. This will be verified by qualitative and quantitative research methods, with the quantitative study being divided into three prospective cross-sectional studies and one interventional study. Data will be obtained from 3240 hospitalized patients by combi-ning subjective methods (questionnaire surveys) and objective measurements (acti-graphy). The project outcomes will allow better understanding of the relationship betwe-en sleep and delirium. A set of non-pharmacological preventive interventions promoting sleep will be developed, with a subsidiary aim to potentially reduce the incidence of delirium in hospitalized patients.