This article historically reviews the limited potential of articular cartilage to heal or regenerate, past emphasis on rest as opposed to motion, and the reasoning that led the author to create the biologic concept of continuous passive motion (CPM) in 1970. The basic premises and hypotheses of CPM are stated. A brief summary is provided of 19 scientific investigations of CPM in rabbits, with particular emphasis on the beneficial short-term and long-term effects of CPM in intra-articular fractures. The conclusions from the basic research are summarized. The clinical applications of CPM to the care of patients are discussed with respect to the indications and the results.