Delirium is defined as an acute change in cognition that cannot be better accounted for by a preexisting or evolving dementia. This form of organ dysfunction commonly occurs in older patients in the emergency department (ED) and is associated with a multitude of adverse patient outcomes. Consequently, delirium should be routinely screened for in older ED patients. Once delirium is diagnosed, the ED evaluation should focus on searching for the underlying cause. Infection is one of the most common precipitants of delirium, but multiple causes may exist concurrently.