The Investigators aim for a 10-month data collection period for TBI patients across the spectrum from concussion to coma with a limited 3-month follow up and extensive 6-, 12-, and 24-month follow ups. Patient enrollment will occur in three high-volume TBI Centers (SFGH, UPMC, UMCB) and a TBI Rehabilitation Center (MSMC). These Centers have a long track record of multi-center TBI research experience as well as existing infrastructure for rapid start-up and sustained enrollment. All patients admitted acutely with a history of external force injury to the head with a head CT performed in the emergency department are eligible for enrollment. Head CTs are performed according to the American College of Emergency Physicians (ACEP) and the Centers for Disease Control and Prevention (CDC) Guidelines for neuroimaging and decision making in TBI. These Guidelines are already in place at the participating Centers and are used to determine which patients will receive a non-contrast head CT scan as part of their initial evaluation. Patients will not be excluded based on age, race, gender, ethnicity, substance abuse, or prior psychiatric history to provide a population-based sample of of TBI subjects across the injury spectrum from concussion to coma.