Delirium is a frequent complication in older patients in the ICU and often persists beyond their ICU stay. Delirium in older persons in the ICU is a dynamic and complex process. There is a high prevalence of pre-existing cognitive impairment in patients who are admitted to the medical ICU. This pre-existing cognitive impairment is an important predisposing risk factor for the development of delirium during and after the ICU stay. Given the high rates of delirium in the ICU that range from 50% to 80% (see references [27, 28, 34]), future studies are urgently needed to examine risk factors for delirium in the ICU setting, such as examining the impact of psychoactive medication use on delirium rates and persistence in the ICU setting. Moreover, studies that examine the impact of delirium prevention in the ICU on rates of delirium, duration and persistence of delirium, and long-term cognitive and functional outcomes post-ICU stay are greatly needed.