Amateur radio (also called ham radio) is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication. The term “amateur” is used to specify persons interested in radio technique solely with a personal aim and without pecuniary interest, and to differentiate it from commercial broadcasting or professional two-way radio services. Amateur radio operation is coordinated by the International Telecommunication Union (ITU) and licensed by national governments that regulate technical and operational characteristics of transmissions and issue individual stations with an identifying call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics and the host government’s radio regulations. Amateurs use a variety of voice, text, image and data communications modes and have access to frequency allocations throughout the RF spectrum to enable communication across a city, a region, a country, a continent or the whole world. An estimated two million people throughout the world are regularly involved with amateur radio.