The ANSI Z136.3 is recognized as the definitive document on laser safety in all health care environments. It provides guidance for the safe use of lasers for medicine, diagnostic, cosmetic, preventative and therapeutic applications in any location where bodily structure or function is altered or symptoms are relieved. Lasers used in these applications are incorporated into an apparatus, which includes a delivery system, a power supply, mechanical housing, and associated liquids and gases as required for operation of the laser. The entire apparatus is referred to as a health care laser system (HCLS), and this standard is intended for use by all personnel associated with the installation, operation, calibration, and maintenance and service of the system. A must for hospitals, medical centers, spas, veterinary offices and clinics using lasers! The Z136.3 was driven by the movement of the widespread use of medical lasers - from hospital operating rooms to the office and/or clinic environment. The use of ophthalmic refractive surgery (excimer) lasers, dermatological lasers and other medical lasers moved from the closely regulated hospital environment into broad applications in conventional medical, surgical and allied professions. The majority of medical laser systems are now found in private medical offices. From this venue they have expanded into cosmetic uses in areas that may have limited or part-time medical supervision, such as in spas and beauty salons. Not only has the environment of these laser systems been greatly broadened, but the training of the people using them has become far more diverse. This rapid change in the pattern of use of health care laser systems has made it essential to have a current document to guide us in the approach to the safe use of these systems. The ANSI Z136.3 represents many necessary compromises to make it fit the needs of this diverse population of users of these medical laser systems. The standard is designed to be used in conjunction with the ANSI Z136.1.