Traumatic brain injury can be defined as the most complex disease in the most complex organ. When an acute brain injury occurs, several pathophysiological cascades are triggered, leading to further exacerbation of the primary damage. A number of events potentially occurring after TBI can compromise the availability or utilization of energy substrates in the brain, ultimately leading to brain energy crisis. The frequent occurrence of secondary insults in the acute phase after TBI, such as intracranial hypertension, hypotension, hypoxia, hypercapnia, hyperthermia, seizures, can then increase cerebral damage, and adversely affect outcome. Neuromonitoring techniques provide clinicians and researchers with a mean to detect and reverse those processes that lead to this energy crisis, especially ischemic processes, and have become a critical component of modern neurocritical care. Which is the best way to monitoring the brain after an acute injury has been a matter of debate for decades. This review will discuss how monitoring the injured brain can reduce secondary brain damage and ameliorate outcome after acute brain injury.