The CN Tower is a telecommunications tower in Toronto, Ontario, Canada. It is 553.33 metres (1,815.39 ft) tall and is the tallest free-standing structure (meaning it cannot have wires to keep it standing) in Canada, North America, and the Western Hemisphere. It is not the tallest building as there are no floors for people to work or live in. That title goes to One World Trade Center in New York City, New York, United States, which is a bit shorter at 1,776 feet (541 m) tall. It is not the tallest structure of any kind in the Americas either, as the KVLY-TV mast in North Dakota, also in the United States, is taller at 2,063 feet (629 m), but that needs wires to keep it upright.
Construction of the concrete tower started on February 6, 1973. In 1975, while it was still being built, it became taller than the Ostankino Tower in Moscow. When it opened to the public on June 26, 1976, it became the tallest free-standing structure on land in the world. It held this record for more than thirty years, until the Burj Khalifa, while it was still being built, became taller on September 12, 2007 . The CN Tower continued to be the world's tallest tower until the Canton Tower became taller in 2010. Now it is the world's third-tallest tower behind the Canton Tower and Tokyo Sky Tree, and fifth tallest free-standing structure behind both of these, the Shanghai Tower, and the Burj Khalifa.
The "CN" in the tower's name came from the Canadian National Railway, the railway company that built the tower. In 1995, the railway sold the tower to the Canada Lands Company (CLC). Local residents wanted to keep the name CN Tower, though, so the abbreviation is now a shortened form of Canada's National Tower instead of the original Canadian National Tower. Neither of these names are commonly used, though; the tower is usually called the CN Tower.