122 Leadenhall Street, which is also known as the Leadenhall Building, is a 225-metre-tall (738 ft) skyscraper in central London. It opened in July 2014 and was designed by the Rogers Stirk Harbour + Partners; it is known informally as The Cheesegrater because of its distinctive wedge shape, similar to that of the kitchen utensil of the same name. It is one of numerous tall buildings recently completed or under construction in the City of London financial district, including 20 Fenchurch Street, 22 Bishopsgate and The Scalpel.

The site is adjacent to the Lloyd's Building, also designed by Rogers, which is the current home of the insurance market Lloyd's of London. Until 2007 the Leadenhall site was occupied by a building owned by British Land and designed by Gollins Melvin Ward Partnership, which was constructed in the 1960s. That building was demolished in preparation for redevelopment of the site. By December 2009 the site was cleared but construction had stalled, initially due to the financial crisis. The project was revived in October 2010 and Oxford Properties co-developed the property in partnership with British Land.

Prior to the site's previous redevelopment in the 1960s, it had been used as the head office of the Peninsular and Oriental Steam Navigation Company (P&O) for over a century. From 1840, P&O had occupied, rent-free, the offices of Willcox & Anderson. However, business east of the Gulf of Suez increased in the late 1840s, so they needed larger offices. In November 1845, the King's Arms inn and hotel at 122 Leadenhall Street was put up for sale. P&O purchased the freehold for £7,250, and then commissioned an architect, Beachcroft, to design a new building. The cost of the new building was estimated at £8,000. In March 1848, P&O moved into the new office.

In 1854, P&O unsuccessfully attempted to purchase the neighbouring building at 121 Leadenhall Street. They eventually took a lease from the charity which held it. They also bought leases of 80 years from St. Thomas's Hospital on the residential properties at Nos. 123, 124 and 125 Leadenhall Street, which were demolished to create a new frontage at No. 122. The new building provided more office space, some of which were for rent, and a spacious new courtyard.

By the mid-1960s P&O needed to redevelop the site to provide increased office space. At the same time, the Commercial Union Assurance Company was planning a redevelopment on an adjacent site on the corner of St Mary Axe. Due to a number of issues affecting both sites, notably poor access to the Commercial Union site and the restricted width of the P&O site, it was not possible to obtain planning consents that would optimise the amount of floor space for both companies. Hence they decided on joint development with the reallocation of site boundaries and the creation of an open concourse area at the junction of Leadenhall Street and St Mary Axe. Both companies would have frontages to the new concourse and would retain site areas equivalent to those enclosed by the original boundaries.

When completed in 1969, the building at 122 Leadenhall Street was 54 m (177 ft) tall with 14 storeys above and three storeys underground. It was originally designed as a pair with the Commercial Union headquarters (now called St. Helen's) by the architects Gollins Melvin Ward Partnership. The two buildings have a central compressional concrete core and have suspended floors that hang using the steel 'chords' visible on the exterior of the building, which are hung from power trusses at the top of the building (and in the case of No. 1 Undershaft, a further central power-truss). It is an example of a tension structure. At the time, it was considered one of the most complex glass-fronted buildings in the United Kingdom. The architect acknowledged the influence of Mies van der Rohe.

The building was extensively damaged by an IRA bomb in the early-1990s and subsequently had to be recladded. It was occupied by various tenants until November 2006, including the Italian International Bank and Calyon.

In 2007–08, the building was demolished to make way for a new development designed by Richard Rogers. The demolition was undertaken by specialist engineering contractor, McGee, with Bovis Lend Lease acting as construction manager. The contract value was £16 million. The first phase of the demolition was conventional: after securing the site, the contractors performed a soft strip of the interior and an asbestos survey prior to demolishing the low-level structures up to podium level. After this, the suspended structure of the building required an unconventional demolition approach that successively dismantled each office floor from the lowest upwards. To achieve this, the contractors installed a structural deck that acted both as a work platform for the demolition work and as a safety barrier. This was jacked upwards as each successive office floor was removed. When all the office floors and upper support trusses had been removed, the concrete core was de-stressed and demolished. Concurrently, the 25,000-cubic-metre (880,000 cu ft) basement was propped and excavated. The contract took just over two years to complete.