Low-back pain (LBP) in active people is common and recurrent. This paper describes: the natural history and clinical course of LBP; anatomy and biomechanics of LBP; what causes pain; diagnosis; initial treatment (e.g., pain and inflammation control, bed rest, and exercises); rehabilitation (e.g., lumbar stabilization exercises, conditioning, and correction of faulty biomechanics); and return to activity. (SM)