Delirium is a common and serious acute neuropsychiatric syndrome and characterized by disturbance in attention and awareness, i.e., reduced ability to direct, focus, sustain, and shift attention and reduced orientation to the environment (Diagnostic and Statistical Manual of Mental Disorders, 5^th edition, American Psychiatric Association, DSM–5, 2013). While delirium is associated with higher rates of mortality and institutionalization, it remains underdiagnosed because of its diverse and multifactorial etiologies and widely variable presentation including hyper– and hypoactive subtypes. Multi–component approaches to modifiable risk factors are recommended for prevention of delirium, which include reduction of benzodiazepines and anti–cholinergic agents and environmental approaches towards normal sleep–wake cycle. Recently, a randomized placebo–controlled trial suggests preventive effects of ramelteon, a melatonin agonist, on delirium. Non–pharmacological strategies are central also for therapy of delirium, which focus on treating the triggering factors and addressing patient–specific and environmental risk factors that may contribute to the development or worsening of delirium. Antipsychotics such as risperidone, quetiapine, olanzapine, perospirone, and haloperidol can be used off–label to manage symptoms of delirium (Clinical Guideline for the Treatment of Delirium, 2^nd edition, Japanese Society of General Hospital Psychiatry, Practice Guidelines 1, 2015).