Tower 42 is the second tallest skyscraper in the City of London, at 25 Old Broad Street. It was originally built for the National Westminster Bank, hence its older name, the NatWest Tower. The tower, designed by Richard Seifert, was built between 1971 and 1979, and opened in 1980, costing a total of £72 million. It is 183m high, which made it the tallest building in the UK until the construction of 1 Canada Square in the Docklands in 1991.

The tower is made with dark colored glass and steel, reflecting the changeable light of London and emerging from the skyline with its particular shape. The building is constructed around a huge concrete core from which the floors are cantilevered, giving it great strength but significantly limiting the amount of office space available.  In June 2012, a Capix LED multi media lighting system was installed around levels 39 to 45. The lighting system is formed of thousands of pixels mounted on a chain netting that is affixed to the surface of the building. Each pixel is formed of three RGB LED units, allowing a variety of lighting designs and colours to be displayed, like  the Olympic Rings during the London 2012 Olympic Games.

On April 24, 1993, the Provisional IRA exploded a huge truck bomb in the Bishopsgate area of the City of London. The bomb extensively damaged the NatWest Tower and many other buildings in the vicinity, causing over £1 billion worth of damage. The tower suffered severe damage and had to be entirely reclad and internally refurbished . After refurbishment, NatWest decided not to re-occupy it, and renamed the building the International Financial Centre, then sold it. The new owners, small UK property company Greycoat, renamed it Tower 42, in reference to its 42 floors. It is now a general-purpose office building occupied by a variety of companies.