Laser therapy, or preferably, Low reactive-Level Laser Therapy (LLLT) is now being recognized as a valid medical tool, with the theories advanced from clinical experiences and double-blind trials being backed up by research data. From its beginnings with Professor Endre Mester’s experiments and clinical trials at the end of the 1960's, LLLT has steadily increased in applications to include an increasing number of medical specialties. The historical background of LLLT is given. The author examines the physical basics of LLLT, and demonstrates the differences between photoactivative laser therapy and photodestructive laser surgery. The α-effect phenomenon of simultaneous LLLT which was reported by early workers in conventional high-powered laser surgery is examined, and the development of pure LLLT is discussed. Wavelength-dependency is discussed, and the importance of methodology is demonstrated. The author discusses the importance of the use of correct terminology in writing or discussing LLLT, and the necessity for accurate and consistent reporting of LLLT therapeutic parameters. Some possible pathways of LLLT are examined, Examples are given showing a wide range of practical multispecialty clinical applications of LLLT, gained from the successful diode laser and combined laser therapy of pure and combined LLLT in over 12 000 patients over the past 13 years. Simultaneous LLLT, concomitant with laser surgery, is not included in these figures.