Delirium is a commonly encountered clinical problem and, contrary to popular belief, should be treated as an acute neurologic emergency. It can be caused by a multitude of conditions and is frequently observed in hospitalized patients. In some cases, delirium results from the direct effect of a toxin, as observed with anticholinergic medications, or from neuronal injury, as seen in herpes simplex virus encephalitis. Because the treatment of delirium rests on the identification and treatment of the underlying illness, the astute clinician must tease apart these various possibilities with a careful history and physical examination and judicious use of laboratory tests and imaging studies. This chapter will review an approach to the patient with delirium and discuss management strategies based on current evidence.