A traumatic brain injury occurs when sufficient force is transmitted to the head to cause damage to the brain and brain function. Direct damage may occur in situations where the skull is fractured or a foreign object penetrates the skull. Indirect brain damage may occur when a force is applied to the head, sufficient to cause the brain to experience forces above normal, resulting in the disruption of normal brain function.

Not all injuries to the brain are traumatic in nature. Things such as lack of oxygen, chemical exposure, lack of blood flow, or infection can cause damage to the brain without any direct trauma. Examples include things such as carbon monoxide exposure or a stroke (cerebrovascular accident/CVA)