Deuterium fluoride (DF) lasers have been under development since about 1970. Their intrinsic ability to store high levels of energy internally plus their ability to quickly dispose of waste heat by the convective flow of exhaust gases make this type of laser attractive to the Army for producing high power levels for an air and missile defense weapon system. This paper reviews the basic principles of a DF laser, the chemistry and spectroscopy associated with producing an excited DF lasing molecule, and the generation of a high power laser beam. This paper also reviews the development history of DF lasers and early lethality demonstrations. This includes a detailed discussion of the Army"s recent Tactical High Energy Laser (THEL) Demonstrator, its architecture and successes during engagements of in-flight rockets and artillery projectiles. The Army is moving forward in developing a new generation, high power DF laser weapon system, the Mobile Tactical High Energy Laser (MTHEL). This system will provide our soldiers protection in the future against a variety of airborne threats.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.