Traumatic brain injury is a leading cause of death by trauma in adults in the United States and a major contributor to permanent physical, emotional, and psychological disabilities. Therapeutic hypothermia, defined as cooling of the body to less than 36 degrees C, has been shown to decrease mortality and morbidity and improve long-term outcomes by protecting the brain from secondary brain injury. The most commonly seen benefits of hypothermic temperatures of 32 degrees C to 33 degrees C are a significant reduction in intracranial hypertension and improved cerebral perfusion and oxygenation. Although evidence to date is insufficient to recommend the routine use of therapeutic hypothermia outside of the research setting, therapeutic hypothermia is used in multiple healthcare facilities in the world. The following article will define hypothermia and provide critical information necessary to provide care for the critically ill patient under therapeutic hypothermia. It will define the processes of brain injury and how hypothermia is thought to counteract those to protect the brain. Also included is a review of 2 major randomized, controlled trials of hypothermia for traumatic brain injury that have been instrumental in establishing guidelines and directing further research.