The major determinant of outcome from traumatic brain injury (TBI) is the severity of the irreversible primary insult. The principles of assessing patients with TBI are based on the ABC approach in common with all trauma victims. This chapter discusses the pathophysiology of intracranial pressure, and outlines monitoring of the injured brain by intracranial pressure monitoring, cerebral oxygenation, EEG and evoked potentials, brain tissue biochemistry and transcranial Doppler ultrasonography. Secondary brain injury results from both systemic and intracranial causes. There is good evidence that protocolized management leads to improved outcome after TBI and may be further improved by treatment within a specialist neurocritical care unit. There has been a shift of emphasis from primary control of intracranial pressure (ICP) to a multifaceted approach of maintenance of cerebral perfusion pressure (CPP) and cerebral protection. Outcome after TBI is usually assessed using the Glasgow Outcome Scale 6 months after injury.