The Warsaw radio mast (pictured), then the tallest structure ever built, at 646.38 metres (2,120.7 ft), collapsed due to an error in exchanging the guys on the highest telecommunications equipment of the mast.

The Warsaw Radio Mast was a radio mast located near Gąbin, Poland, and was the world's tallest structure at 2,120 ft from 1974 until its collapse on 8 August 1991. The mast was designed for extreme height in order to broadcast Polish state media around the world, including to the remotest areas such as Antarctica. As of 2023, it was the third-tallest artificial structure ever built, after the Burj Khalifa tower in the United Arab Emirates in 2009, and Merdeka 118 tower in Malaysia in 2022.

The tallest structure in the world is the Burj Khalifa skyscraper at 828 m (2,717 ft). Listed are guyed masts, self-supporting towers, skyscrapers, oil platforms, electricity transmission towers, and bridge support towers. This list is organized by absolute height. See History of the world's tallest structures, Tallest structures by category, and List of tallest buildings for additional information about these types of structures.

A guy-wire, guy-line, guy-rope, down guy, or stay, also called simply a guy, is a tensioned cable designed to add stability to a freestanding structure. They are used commonly for ship masts, radio masts, wind turbines, utility poles, and tents. A thin vertical mast supported by guy wires is called a guyed mast. Structures that support antennas are frequently of a lattice construction and are called "towers". One end of the guy is attached to the structure, and the other is anchored to the ground at some distance from the mast or tower base. The tension in the diagonal guy-wire, combined with the compression and buckling strength of the structure, allows the structure to withstand lateral loads such as wind or the weight of cantilevered structures. They are installed radially, usually at equal angles about the structure, in trios and quads. As the tower leans a bit due to the wind force, the increased guy tension is resolved into a compression force in the tower or mast and a lateral force that resists the wind load. For example, antenna masts are often held up by three guy-wires at 120° angles. Structures with predictable lateral loads, such as electrical utility poles, may require only a single guy-wire to offset the lateral pull of the electrical wires at a spot where the wires change direction.