One Canada Square is a skyscraper in Canary Wharf, London. It is the third tallest building in the United Kingdom at 770 feet (235 m) above ground level, and contains 50 storeys. It achieved the title of the tallest building in the UK upon completion in 1991 and held the title for 21 years until the completion of The Shard (310m) in 2012.

One Canada Square was designed by César Pelli with Adamson Associates and Frederick Gibberd Coombes. The building is clad with stainless steel. One of the predominant features of the building is the pyramid roof, which contains a flashing aircraft warning light, a rare feature for buildings in the United Kingdom. The distinctive pyramid pinnacle is 800 feet (240 m) above sea level.

One Canada Square is primarily used for offices, though there are some retail units on the lower ground floor. There is no observation floor. It is a prestigious location for offices and as of October 2017 was completely let. The building is recognised as a London landmark, and it has gained much attention through film, television, and other media as one of the tallest buildings in the United Kingdom.