The ability of laser irradiation to destroy tissue is well known. Less well known is the fact that the same radiation, at much lower intensities, can non-destructively alter cellular function. This latter phenomenon, which occurs in the absence of significant heating, is now a basis for the conservative treatment of a variety of musculoskeletal, neurological, and soft tissue conditions in many parts of the world. This review first examines the 25-year history and scientific basis of "laser therapy." Clinical applications are discussed and the reasons for its relative lack of acceptance in the US are examined. The article concludes with an overview of current research and the impact it will have on laser therapy's role in US clinical practice.