The BT Tower is a communications tower in Fitzrovia, London, England, constructed in 1964. At the time of its completion it was known as the Museum Radio Tower, referring to its use by the neighbouring Museum Telephone Exchange. Subsequent changes in ownership caused it to become the Post Office Tower and Telecom Tower before it gained its current name in 1991. Since 2024 it has been owned by MCR Hotels. In 2003 Historic England designated it as a Grade II listed building.

The main structure is 177 metres (581 ft) high, with aerial rigging bringing the total height to 189 metres (620 ft).Upon completion it was the tallest structure in London and remained so until 1980. Butlins managed a revolving restaurant in the tower from 1966 until 1980. A 360° LED screen displays news across central London.

The tower was commissioned by the General Post Office (GPO). Its primary purpose was to support the microwave aerials then used to carry telecommunications traffic from London to the rest of the country, as part of the GPO microwave network.

It replaced a shorter, 1940s steel lattice tower on the roof of the Museum Telephone Exchange, so named for its proximity to the British Museum. The taller structure was required to protect the radio links' line of sight against tall buildings then planned in London. Links were routed via GPO microwave stations Harrow Weald, Bagshot, Kelvedon Hatch and Fairseat, and locations including the London Air Traffic Control Centre.

The tower was designed by the Ministry of Public Building and Works, under chief architects Eric Bedford and G R Yeats. Typical for its time, the building is concrete clad in glass. The narrow cylindrical shape was chosen as a stable platform for microwave aerials. It shifts no more than 25 centimetres (10 in) in wind speeds of up to 150 km/h (95 mph). To prevent overheating, the glass cladding had to be tinted.

Construction began in June 1961; owing to the building's height and its having a tower crane jib across the top virtually throughout the whole construction period, it gradually became a very prominent landmark that could be seen from almost anywhere in London. A question was raised in Parliament in August 1963 about the crane. Reginald Bennett MP asked the Minister of Public Buildings and Works, Geoffrey Rippon, how, when the crane on the top of the new Tower had fulfilled its purpose, he proposed to remove it. Rippon replied: "This is a matter for the contractors. The problem does not have to be solved for about a year but there appears to be no danger of the crane having to be left in situ." Construction reached 475 ft by August 1963. The revolving restaurant was prefabricated by Ransomes & Rapier and the lattice tower by Stewarts & Lloyds subsidiary Tubewrights.

The tower was topped out on 15 July 1964, by Geoffrey Rippon and inaugurated by Prime Minister Harold Wilson on 8 October 1965. The main contractor was Peter Lind & Company.

The tower was originally designed to be just 111 metres (364 ft) high; its foundations are sunk down through 53 metres (174 ft) of London clay, and are formed of a concrete raft 27 metres (89 ft) square, 1 metre (3 ft) thick, reinforced with six layers of cables, on top of which sits a reinforced concrete pyramid.