Although medical management of traumatic brain injury (TBI) may have improved in developed countries, TBI is still a major cause of mortality and morbidity. The demographics are skewed towards the younger patient population, and affects males more than females, but in general follow a bimodal distribution with peaks affecting young adults and the elderly. As a result, the loss of functional years is devastating. Pathology due to brain trauma is a complex two-hit phenomenon, frequently divided into ‘primary’ and ‘secondary’ injury. Hypoxia, ischaemia, and inflammation all play a role, and the importance of each component varies between patients and in an individual patient over time. The initial injury may increase intracranial pressure and reduce cerebral perfusion due to the presence of mass lesions or diffuse brain swelling. Further secondary insults, such as hypotension, reduced cerebral perfusion pressure, hypoxia, or fever may exacerbate swelling and inflammation, and further compromise cerebral perfusion. Although there are currently no specific effective treatments for TBI, an improved understanding of the pathophysiology may eventually lead to treatments that will reduce mortality and improve long-term functional outcome.