Pain can be an adaptive sensation, an early warning to protect the body from tissue injury. By the introduction of hypersensitivity to normally innocuous stimuli, pain may also aid in repair after tissue damage. Pain can also be maladaptive, reflecting pathological function of the nervous system. Multiple molecular and cellular mechanisms operate alone and in combination within the peripheral and central nervous systems to produce the different forms of pain. Elucidation of these mechanisms is key to the development of treatments that specifically target underlying causes rather than just symptoms. This new approach promises to revolutionize pain diagnosis and management.