Shock is a life-threatening condition of circulatory failure leading to inadequate organ perfusion and tissue oxygenation. In a trauma patient, shock may be due to hypovolemia, cardiogenic, obstructive or distributive causes individually or in combination. The physiological response to major hemorrhage is dependent on a variety of autonomic reflexes, mechanism of injury, bleeding source, and baseline physiology of the patient. This article discusses the common causes of shock and the accompanying physiology, how clinical assessment can support the diagnosis and effective treatment of shock, and the common pitfalls in trauma patients.