When looking at all of the wireless devices and applications that are possible, from radio astronomy to cell phones, it quickly becomes clear that there must be rules on how to use the limited radio spectrum. If not, the airwaves would be a jumble of hundreds of applications all interfering with each other. In the United States, the Federal Communications Commission (FCC) is responsible for the regulation of all RF devices. The FCC requires any device that radiates RF energy to be tested for compliance with the FCC rules. These rules are contained in the Code of Federal Regulations, Title 47. Part 15 is the section of the code that deals with devices that do not require the user to have an individual license. These regulations are available on the FCC website and it is recommended that they be reviewed prior to starting an RF design.