Severe traumatic brain injury is a complex disease that involves physical injury and distortion of tissues and cell membranes, gross hemodynamic changes including loss of autoregulation, cerebral edema and tissue shifts, changes in pressure and perfusion and multiple secondary cellular processes including electrolyte fluxes, inflammatory mediator release, neurotransmitter mediated excitotoxicity, apoptosis, mitochondrial dysfunction, and alterations in cellular metabolism. The optimal treatment of these patients who have severe neurological dysfunction or require sedation that compromises neurological functional assessment by physical examination requires the monitoring and management of multiple aspects of brain physiology including pressure, perfusion, oxygenation, cellular metabolism, and electrical activity. Invasive monitoring techniques, while still in various stages of development, can and will provide real-time trackable data that informs the management of these patients as well as contributes to our understanding of the pathophysiological processes that contribute to it.