Delirium is a complex neuropsychiatric syndrome characterized by disturbances in consciousness, orientation, memory, thought, perception, and behaviour due to one or more structural and/or physiological abnormalities directly or indirectly affecting the brain. It is quite prevalent in medical and surgical settings and is associated with high rates of death and healthcare costs. We review its prevalence, clinical features, risk factors, pathogenesis, assessment instruments, differential diagnosis, management, prognosis and prevention. Special emphasis is given on the Indian research, which is quite meagre.