CQ is a code used by wireless telegraphy operators, particularly those communicating in Morse code, but also by voice operators, to make a general call (called a CQ call). Transmitting the letters CQ on a particular channel is an invitation for any operators listening on that channel to respond.
A CQ call can be qualified by appending more letters, as in CQ DX (meaning 'calling all long-distance stations'), or the ITU callsign prefix for a particular country (e.g. CQ VK for 'calling Australia'). The originator of the call can be identified by appending the letters DE (French for 'from', also means 'this is...') and the callsign of the transmitting station.
A variant of the CQ call, CQD, was the first code used as a distress signal. It was proposed by the Marconi Company and adopted in 1904, but was replaced between 1906 and 1908 by the SOS code. However, when the Titanic sank in 1912, it transmitted the distress call CQD DE MGY, MGY being the ship's callsign.
The CQ call was originally used by landline telegraphy operators in the UK. French was, and still is, the official language for international postal services, and the word sÚcuritÚ was used to mean 'safety' or 'pay attention'. It is still used in this sense in international telecommunications. The letters CQ, when pronounced in French, resemble the first two syllables of sÚcuritÚ, and were therefore used as shorthand for the word. In English-speaking countries, the origin of the abbreviation was popularly changed to the phrase "seek you", or later, when used in the CQD distress call, to the command "come quick". CQ was adopted by the Marconi company in 1904 for use in wireless (spark) telegraphy, and was adopted internationally at the 1912 London Radiotelegraph Convention, and is still used.
CQ is also the alternate title of Congressional Quarterly a publication that summarizes the legislative activities of the United States Congress.
CQ (2001) is a film directed by Roman Coppola and starring Jeremy Davies and Angela Lindvall.