The Warsaw radio mast was the world's tallest structure until its collapse on 8 August 1991. It is the second tallest land-based structure ever built, being surpassed as tallest by the Burj Khalifa, completed in 2010.

The mast, which was designed by Jan Polak, was 646.38 metres (2,120.67 ft) tall. Its construction, started in July 1970, was completed on 18 May 1974, and its transmitter entered regular service on 22 July of that year. It was located in Konstantynów, Gąbin, Poland, and was used by Warsaw Radio-Television (Centrum Radiowo-Telewizyjne) for longwave radio broadcasting on a frequency of 227 kHz before 1 February 1988 and 225 kHz afterwards. Its base, according to Google Earth, was 115.2 metres above sea level. Because a voltage potential of 120 kV was desired between the mast and ground, it stood on a 2-metre-high insulator. It operated as a mast radiator (half wave radiator), so its height was chosen in order to function as a half-wavelength antenna at its broadcasting frequency. The signals from its 2 megawatt transmitters could be received across all of Europe, North Africa and as far away as North America. Its weight is debated: 380 tonnes, 420 tonnes, 550 tonnes and even 660 tonnes have been cited, probably the result of inaccurate unit conversions by translators. Polish sources claim 420 tonnes.

Warsaw (Polish: Warszawa [varˈʂava] ( listen); see also other names) is the capital and largest city of Poland. It is located on the Vistula River, roughly 260 kilometres (160 mi) from the Baltic Sea and 300 kilometres (190 mi) from the Carpathian Mountains. Its population in 2010 was estimated at 1,716,855 residents with a greater metropolitan area of 2,631,902 residents, making Warsaw the 10th most populous city proper in the European Union. The area of the city covers 516.9 square kilometres (199.6 sq mi), while the city's agglomeration covers 6,100.43 square kilometres (2,355.39 sq mi).

Warsaw is an Alpha- global city, a major international tourist destination and an important economic hub in Central Europe. It is also known as the "phoenix city" because it has survived many wars throughout its history. Most notably, the city had to be painstakingly rebuilt after the extensive damage it suffered from World War II, during which 80% of its buildings were destroyed. On 9 November 1940 the city was awarded Poland's highest military decoration for heroism, the Virtuti Militari, for the Siege of Warsaw (1939).

Radio masts and towers are, typically, tall structures designed to support antennas (also known as aerials) for telecommunications and broadcasting, including television. They are among the tallest man-made structures. Similar structures include electricity pylons and towers for wind turbines.

Masts are sometimes named after the broadcasting organisations that use them, or after a nearby city or town.

The Warsaw Radio Mast was the world's tallest supported structure on land, but it collapsed on August 8, 1991, leaving the KVLY/KTHI-TV mast as the tallest.

In the case of a mast radiator or radiating tower, the whole mast or tower is itself the transmitting antenna.

The terms "mast" and "tower" are often used interchangeably. However, in structural engineering terms, a tower is a self-supporting or cantilevered structure, while a mast is held up by stays or guys. Broadcast engineers in the UK use the same terminology. In US broadcast engineering, a tower is an antenna structure attached to the ground, whereas a mast is a vertical antenna support mounted on some other structure (which itself may be a tower, a building, or a vehicle). Masts (to use the civil engineering terminology) tend to be cheaper to build but require an extended area surrounding them to accommodate the guy wires. Towers are more commonly used in cities where land is in short supply.