This document defines and discusses head injuries. It notes that in the US there are 500,000 new head injury cases annually, with 10% dying before reaching the hospital. Head injuries are classified based on their mechanism, severity using the GCS score, morphology, and whether they are primary or secondary injuries. The anatomy of the head and mechanisms of secondary injuries like hematomas are described. Management involves thorough history, physical exam, imaging studies, and specific treatments depending on injury type and severity ranging from observation to surgery.