The last few years there has been increased interest in the commercialization of the Global Navigation Satellite System (GNSS) which is often referred to as the Global Positioning System (GPS) in various applications. A GPS system uses spread spectrum signals-binary phaseshift keying (BPSK)-emitted from satellites in space for position and time determinations. Until recently, the use of GPS was essentially reserved for military use. Now there is great interest in using GPS for navigation of commercial aircraft. The U.S. Federal Aviation Administration (FAA) is looking into the possibility of using a wide area augmentation system (WAAS) to cover the whole United States with one system. There are also applications in the automotive industry, surveying, and personal and recreational uses. Due to the increase in popularity of GPS, and since it is a spread spectrum communication system using BPSK, a brief introduction is included in this text.