The authors describe the use of GPS (Global Positioning System) for time coordination. When GPS first became available, it provided a quantum leap in time coordination with little or no effort on the part of the user. However, workers realized that with more sophisticated analysis techniques even greater accuracy could be wrung from GPS. The authors describe the level of time coordination these more sophisticated techniques have affected. The principles of GPS time transfer are described with emphasis on the so-called common view method. The sources of error during GPS time transfer are discussed and the various possibilities of reducing them are investigated. Some possibilities for overcoming SA (selective availability of GPS) are also discussed. GPS is additionally shown to be an outstanding tool for the dissemination of Coordinated Universal Time (UTC). >