For many millennia the record holder for world's tallest structure was clearly defined (see table below.) However, there has been much debate as to the ranking of the world's tallest structures since the middle of the 20th century, chiefly depending on the criteria used for selecting the structures admissible to the list.

In particular, there is debate about whether:

• guy-wire-supported structures can be counted,
• only habitable height counts,
• roof-top antennas can be counted towards height of inhabitable buildings; the debate over this originates from that fact that spires are included in the height but antennas are not (see the debate on the Sears Tower versus the Petronas Towers),
• observation galleries on communication towers make them into habitable buildings,
• structures under construction can be included in the list, and whether
• structures rising out of water should have their below-water height included.

Tallest structures

KVLY-TV mast

Tallest Structure by Category

The tallest currently standing structure is the KVLY-TV mast near Mayville, North Dakota, at 629 m (2,063 ft). It is a transmission antenna, consisting of a bare metal structure supported by guy-wires. Transmission towers in excess of 600 meters (~2000 ft) are common in the American Midwest; similar structures exist near Alleman, Iowa and Rapid City, South Dakota.

The Warsaw radio mast near Warsaw, Poland at 645 m (2,115 ft) was taller, but it collapsed in 1991.

The main reason these transmission antennas are not usually included with the world's tallest buildings is that they are not self-supported. Another example of a structure that's not self-supporting is a long rope tethered to the ground on one end and to a helium balloon on the other. If structures that are not self-supporting were counted then these would be the tallest in the world.

The Petronius Platform stands 610 m (2,001 ft) tall, making it the tallest freestanding structure in the world. However, as this oil and natural gas platform is partially supported by buoyancy, some critics argue that the below-water height should not be counted, in the same manner as the underground 'height' of buildings is not taken into account.

The CN Tower in Toronto stands 553.33 m (1,815 ft) tall, making it the tallest freestanding structure above ground. Ostankino Tower in Moscow is currently being renovated following a fire. When completed it will stand 577m (1,893 ft).

Tallest buildings

Comparison of top skyscrapers

Up until 1998 the tallest building status was essentially uncontested. Counting buildings as structures with floors throughout, New York City's World Trade Center was the tallest including the antennas, Sears Tower in Chicago excluding the antennas. As antennas were usually excluded, Sears Tower was counted as the tallest. When Petronas Twin Towers in Kuala Lumpur, Malaysia was built, some felt that the "spire" extending to 9 meters higher than the roof of the Sears Tower was just added to "cheat" its way into the spot as tallest building. Excluding the spire, the Petronas Towers were not taller than the Sears Tower. Therefore, the Council on Tall Buildings and Urban Habitat defined four categories in which the "world's tallest building" can be measured:

1. Height to the structural or architectural top (including spires and pinnacles, but not antennas, masts or flagpoles)
2. Height to the highest occupied floor
3. Height to the top of the roof
4. Height to the top of antenna

The height is measured from the sidewalk level of the main entrance. In all of these categories, Sears Tower had held the top spot. After Petronas was built, Sears Tower became second in the first category only.

As of April 20, 2004, Taipei 101 in Taipei, Taiwan leads in the first category with 508 m (1,667 ft); in the second category with an occupied floor at 438 m (1,437 ft); and in the third category with 448 m (1,470 ft). The first category was formerly held by the Petronas Twin Towers with 452 m (1,483 ft), and before that by Sears Towers with 443 m (1,448 ft). The second category was held by the Sears Tower, with 435 m (1,431 ft). The third category was formerly held by the Sears Tower with 442 m (1,445 ft).

The Sears Tower still leads in the fourth category with 529 m (1,736 ft), previously held by the World Trade Center until its destruction in 2001; its antenna included, it measured 536 m (1,758 ft). The World Trade Center became the world's tallest buildings to be demolished–indeed, its site entered the record books twice on September 11, 2001, in that category, replacing the Singer Building, which once stood a block from the WTC site.

The CN Tower is excluded from these categories because it is not a "habitable building", which is defined as a frame structure made with floors and walls throughout.

History of Record Holders in each CTBUH category

Tallest structures before 1954

Currently-standing tallest structures

¹ Height for inhabited buildings (with stories) does not include TV towers and antennae.

Source: Council on Tall Buildings and Urban Habitat.