The task of medicine is to preserve and restore health and to relieve suffering. Understanding pain is essential to both these goals. Because pain is universally understood as a signal of disease, it is the most common symptom that brings a patient to a physician’s attention. The function of the pain sensory system is to protect the body and maintain homeostasis. It does this by detecting, localizing, and identifying tissue-damaging processes. Since different diseases produce characteristic patterns of tissue damage, the quality, time course, and location of a patient’s pain complaint and the location of tenderness provide important diagnostic clues and are used to evaluate the response to treatment. Once this information is obtained, it is the obligation of the physician to provide rapid and effective pain relief.