A numbers station is a shortwave radio station characterized by broadcasts of formatted numbers, which are believed to be addressed to intelligence officers operating in foreign countries.[1] Most identified stations use speech synthesis to vocalize numbers, although digital modes such as phase-shift keying and frequency-shift keying, as well as Morse code transmissions, are not uncommon. Most stations have set time schedules, or schedule patterns; however, some appear to have no discernible pattern and broadcast at random times. Stations may have set frequencies in the high-frequency band.[2]

Numbers stations have been reported since at least the start of World War I and continue in use today. Amongst amateur radio enthusiasts there is an interest in monitoring and classifying numbers stations, with many being given nicknames to represent their quirks or origins.