Since the development of the ruby laser by Maiman in 1960 and the application of the laser for endodontics by Weichman in 1971, a variety of lasers with a wide range of characteristics are now being used in endodontic therapy. In the past two decades much experience and knowledge has been gained The first purpose of the present paper is to provide an understanding of the essential physical science behind laser technology and information on the effects of laser beams on tissue (tissue interaction). A second purpose is to summarize laser applications in endodontics, including their use in pulp diagnosis, dentinal hypersensitivity, pulp capping and pulpotomy, modification of the root canal walls, sterilization of the root canal system, cleaning--shaping--obturation of the root canal, and endodontic surgery. It will be clear that a number of endodontic procedures with conventional treatments cannot provide comparable results or are less effective.