Delirium is a common condition, and is associated with adverse outcomes, including increased morbidity, increased mortality, and increased health services utilization. However, no medications against delirium have yet been approved. Thus, delirium is still unexplored not only in the psychiatric field, but also in all medical services. In the review, delirium etiologies, prediction, diagnosis, prevention, and treatment are outlined. Especially, future strategies of prediction and prevention, and the evaluation of antipsychotics from a safety perspective, are presented. On the basis of such points, a treatment algorithm is proposed.