Spinal manipulative therapy is growing in popularity and acceptance, as judged by the increasing number of practitioners in physical therapy and medicine and by the results of clinical trials. Manipulation is the skilled, gentle, passive movement of a joint (or spinal segment) either within or beyond its active range of motion. This definition is broad enough to encompass a great variety of techniques, ranging from the more traditional thrust to oscillation and distraction. Manipulation is rendered effective by a combination of mechanical, neurophysiologic, and biomechanical mechanisms.