Traumatic brain injury (TBI) is a leading cause of death after injury in the United States (Baker et al., Am J Surg 140:144–150, 1980). Prompt recognition and sound patient management can alter clinical trajectory and result in significant improvements in outcomes. Evaluation of each patient in the context of their multiorgan injury pattern is essential. A keen understanding of relevant anatomy and physiology is the basis for clinical suspicion, diagnostic workup, and implementation of therapeutic interventions. As available imaging, monitoring, and therapeutic options expand, so too does the necessity for thoughtful selection and application of such modalities to a given TBI patient. This chapter aims to review the basic concepts critical to understanding TBI, providing a framework for TBI classification and treatment as it stands today.