Concussion and mild traumatic brain injury (mTBI) are common clinical problems. However, the literature is not consistent in defining how concussion and mTBI are related. Although most patients with concussion recover within days to weeks, approximately 10% develop persistent signs and symptoms of post-concussion syndrome (PCS). There are no scientifically established treatments for concussion or PCS and thus rest and cognitive rehabilitation are traditionally applied, with limited effectiveness. This article presents a clinical model to suggest that concussion evolves to become mTBI after PCS has developed, representing a more severe form of brain injury. The basic pathophysiology of concussion is presented, followed by a recommended approach to the clinical evaluation of concussion in the emergency department and the physician's office. We evaluate the limited evidence-based pharmacologic treatment of acute concussion symptoms and PCS symptoms and also discuss return to activity recommendations, with an emphasis on athletes. Lastly, we suggest a promising new direction for helping patients recover from PCS.