This monograph summarizes current knowledge related to the diagnosis, epidemiology, etiology, and management of delirium. The monograph is based on the guideline ‘delirium’ of the National Institute of Clinical Excellence (NICE) , as well as on systematic reviews and pivotal trials. The quality of the evidence discussed in this monograph is graded as ‘high,’ ‘moderate,’ ‘low’ or ‘very low,’ following the ‘Grading of Recommendations Assessment, Development and Evaluation’ (GRADE) system, which was developed by the Cochrane Center (www.igh.org/Cochrane/GRADE). Readers are encouraged to consult the recommended readings for more detailed information (see: web-appendices).