There are no age, citizenship, or license requirements to operate a CB radio in the United States, and the service falls under the "License by Rule" part of the FCC rules (basically, if one follows the rules one is considered licensed). Operators may use any of the authorized 40 CB channels; however, channel 9 is used only for emergency communications or for traveler assistance and the higher number channels are almost exclusively SSB modulation. Use of all channels is on a shared basis. However, foreign governments and their representatives are not eligible to use citizens' band radio within the United States.