Acute and chronic pain are different clinical entities. Acute pain is provoked by a specific disease or injury, serves a useful biologic purpose, is associated with skeletal muscle spasm and sympathetic nervous system activation, and is self-limited. Chronic pain, in contrast, may be considered a disease state. It is pain that outlasts the normal time of healing, if associated with a disease or injury. Chronic pain may arise from psychological states, serves no biologic purpose, and has no recognizable end-point. Both acute and chronic pain are an enormous problem in the United States, costing 650 million lost workdays and $65 billion a year. The therapy of acute pain is aimed at treating the underlying cause and interrupting the nociceptive signals. The therapy of chronic pain must rely on a multidisciplinary approach and should involve more than one therapeutic modality.