Maintenance of brain perfusion and oxygenation is of paramount importance to patient outcome with various types of brain injuries (traumatic, ischemic, and hemorrhagic). Historically, monitoring of intracranial pressure and cerebral perfusion pressure has been the mainstay of neuromonitoring techniques used at the critical care bedside to monitor brain perfusion and oxygenation. This article describes the bedside neuromonitoring techniques that have emerged for use with these patients in the critical care area. To give the reader an understanding of the functionality of these neuromonitoring techniques, the article first summarizes the physiology of brain perfusion and oxygenation.