Delirium is an acute confusional state that is common and costly and is associated with significant functional decline and distress. It is the manifestation of acute encephalopathy and is variably called acute brain failure, acute brain dysfunction, or altered mental status. All patients are at risk for delirium, although those with more vulnerabilities (such as advanced age, exposures to other stressors like infection, and certain medications) are at higher risk. The pathophysiologic cause of delirium is not well understood. It is important to recognize patients at risk for and those with delirium and to immediately identify and treat factors contributing to it. There is no single intervention or medication to treat delirium, making it challenging to manage. Therefore, risk mitigation and prompt treatment rely on a sophisticated strategy to address the contributing factors. Delirium may be prevented or attenuated when multimodal strategies are used, thereby improving patient outcomes.