A traumatic brain injury (TBI), also known as an intracranial injury, is an injury to the brain caused by an external force. TBI can be classified based on severity (ranging from mild traumatic brain injury [mTBI/concussion] to severe traumatic brain injury), mechanism (closed or penetrating head injury), or other features (e.g., occurring in a specific location or over a widespread area). Head injury is a broader category that may involve damage to other structures such as the scalp and skull. TBI can result in physical, cognitive, social, emotional and behavioral symptoms, and outcomes can range from complete recovery to permanent disability or death. Causes include falls, vehicle collisions and violence. Brain trauma occurs as a consequence of a sudden acceleration or deceleration within the cranium or by a complex combination of both movement and sudden impact. In addition to the damage caused at the moment of injury, a variety of events following the injury may result in further injury. These processes include alterations in cerebral blood flow and pressure within the skull. Some of the imaging techniques used for diagnosis include computed tomography (CT) and magnetic resonance imaging (MRIs). Prevention measures include use of seat belts and helmets, not drinking and driving, fall prevention efforts in older adults and safety measures for children. Depending on the injury, treatment required may be minimal or may include interventions such as medications, emergency surgery or surgery years later. Physical therapy, speech therapy, recreation therapy, occupational therapy and vision therapy may be employed for rehabilitation. Counseling, supported employment and community support services may also be useful. TBI is a major cause of death and disability worldwide, especially in children and young adults. Males sustain traumatic brain injuries around twice as often as females. The 20th century saw developments in diagnosis and treatment that decreased death rates and improved outcomes. Classification Traumatic brain injury is defined as damage to the brain resulting from external mechanical force, such as rapid acceleration or deceleration, impact, blast waves, or penetration by a projectile. Brain function is temporarily or permanently impaired and structural damage may or may not be detectable with current technology. TBI is one of two subsets of acquired brain injury (brain damage that occur after birth); the other subset is non-traumatic brain injury, which does not involve external mechanical force (examples include stroke and infection). All traumatic brain injuries are head injuries, but the latter term