Cerebrovascular disease and trauma are leading causes of death in the United States. In addition to the initial insult to the brain, disturbances of cerebral oxygenation and metabolism underlie many of the secondary pathophysiological processes that increase both morbidity and mortality. Therefore, researchers and clinicians have sought to obtain a more thorough understanding of the physiological and biochemical principles of cerebral oxygenation and metabolism. New technologies capable of offering continuous and quantitative assessment of cerebral oxygenation may improve clinical outcomes. In this article, we review the physiological principles of cerebral metabolism, cerebral blood flow and their metabolic coupling, and cerebral oxygenation, with particular emphasis on variables that could be monitored and managed in an intensive care unit setting.