The hospital is not conducive to sleep. Patients in the ICU are particularly susceptible to sleep disruption secondary to environmental and medical issues. Despite the frequency of sleep disruption in the ICU, the quality of critically ill patients' sleep is often overlooked. This article discusses the following issues essential to understanding the factors associated with sleep loss in the ICU: (1) core elements to consider from the baseline sleep history, (2) impact of the ICU environment on the ICU patient's sleep pattern, and (3) overall systematic impact of sleep deprivation on the ICU patient.