Delirium is associated with a prolonged ICU stay, a greater risk of death during ICU stay, and a poorer prognosis after discharge. Guidelines with comprehensive recommendations are available for the management of delirium in the ICU, including the management of pain and agitation, using an integrated and multidisciplinary approach. However, these guidelines are not routinely used in clinical practice despite their proven benefit. Implementation science offers tools and processes to improve the routine use of guidelines. The aim of the study described in this thesis was to investigate various aspects of the implementation of delirium guidelines. This study was coined the ‘ICU Delirium in Clinical Practice Implementation Evaluation’ (iDECePTIvE) study, and six ICU departments from the South-West Netherlands region participated.