Grosvenor Square /ˈɡroʊvnər/ is a large garden square in the Mayfair district of Westminster, Greater London. It is the centrepiece of the Mayfair property of the Duke of Westminster, and takes its name from the duke's surname "Grosvenor". It was developed for fashionable residences in the 18th century. In the 20th it had an American and Canadian diplomatic presence, and currently is mixed use, commercial.
Sir Richard Grosvenor obtained a licence to develop Grosvenor Square and the surrounding streets in 1710,  and development took place between 1725 and 1731. The land was sold in individual plots, with 30 different builders or partnerships taking a lease; about half of these had become bankrupt by 1738.  Grosvenor Square was one of the three or four most fashionable residential addresses in London from its construction until the Second World War, with numerous leading members of the aristocracy in residence. 
The early houses were generally of five or seven bays, with basement, three main stories and an attic. Some attempt was made to produce impressive groupings of houses, and Colen Campbell produced a design for a palatial east side to the square featuring thirty Corinthian columns but this was not carried out and in the end most of the houses were built to individual designs. There were mews behind all four sides.
Many of the houses were rebuilt later in the 18th century or during the 19th century, generally acquiring an extra storey when this happened. Number 23 (later 26) was rebuilt in 1773–74 for the 11th Earl of Derby by Robert Adam, and is regarded as one of the architect's finest works and as a seminal example of how grandeur of effect and sophisticated planning might be achieved on a confined site. It was demolished and rebuilt again in the 1860s. Nearly all of the older houses were demolished during the 20th century and replaced with blocks of flats in a neo-Georgian style, hotels and embassies.
Providing almost 2.5 hectares of open garden, Grosvenor Square is the second-largest garden square in central London after Russell Square at 2.5 hectares. While Lincoln's Inn Fields at 4.5 hectares is a larger space, it is categorised as an Inn of Court, not a garden square.
Grosvenor Square was originally laid out by gardener John Alston in the 1720s; his 'wilderness worke' design was a celebration of the countryside in the city. However, the gardens have been modified over time to meet the changing needs of those around them. Reserved for residents' use for much of its life, the Grade II-registered landscape  was, after the Second World War, made a public space for everyone's enjoyment, through the Roosevelt Memorial Act.  It was then managed by the Royal Parks until 2018, when Grosvenor Britain & Ireland took over its management.
Following an international Call for Ideas in 2018,  Grosvenor confirmed that the square would be redesigned to enhance its contribution to the environment and local communities.  In June 2022, Westminster City Council approved a proposal to transform the square into "an extraordinary garden with groundbreaking environmental credentials". It is expected that, once started, the works would take around two years to complete. 
In the 1920s, four of the "Bentley Boys" – Woolf Barnato, Tim Birkin, Glen Kidston and Bernard Rubin – took adjacent flats in the fashionable south-east corner of the square, where their day-long parties became something of social legend. So common was the sight of their large, green sports cars parked ad hoc outside their flats, that for many years London cab drivers referred to the spot as "Bentley Corner".
Grosvenor Square was long a center of American presence in London beginning when John Adams established the first American mission to the Court of St. James's in 1785. Adams lived, from 1785 to 1788, in the house which still stands on the corner of Brook and Duke Streets.
During the Second World War American general Dwight D. Eisenhower established a military headquarters at 20 Grosvenor Square, and during this time the square was nicknamed "Eisenhower Platz".  Until 2009, the United States Navy continued to use this building as its headquarters for United States Naval Forces Europe. A statue of wartime president Franklin D. Roosevelt sculpted by Sir William Reid Dick stands in the square, as does a later statue of Eisenhower, and a statue of president Ronald Reagan.  The square also contains the Eagle Squadrons Memorial.
The former United States Embassy of 1938–1960 on the square was purchased by the Canadian government and renamed Macdonald House. It was part of the Canadian High Commission in London until 2014, when all the functions of the Canadian High Commission were transferred to Canada House in Trafalgar Square.
In 1960, a new United States Embassy was built on the western side of Grosvenor Square. This was a large and architecturally significant modern design by Eero Saarinen, being at the time a controversial insertion into a mainly Georgian and neo-Georgian district of London. In March and October 1968, there were large demonstrations in the square against US involvement in the Vietnam War. On both occasions, the protest became violent.  After 2001 a series of anti-terrorist devices were installed around the embassy, and the road running along the front of the building was closed completely to traffic. In 2006, the Grosvenor Square Safety Group residents association took out advertisements in The Washington Post and The Times , accusing the Metropolitan Police and local government of a "moral failure" for not closing two other roads adjacent to the embassy. 
In 2008, the United States Government chose a site for a new embassy in the Nine Elms area of the London Borough of Wandsworth, south of the River Thames. Construction of the new Embassy of the United States in London began in 2013, with relocation completed by 2017. In October 2009, following a recommendation by English Heritage, the Saarinen designed building was granted Grade II listed status.  The listing means that the new owners will not be allowed to change the facade, which includes the 35-foot-wingspread gilded-aluminium eagle that hovers above the main entrance. In November 2009, the Grosvenor Square property was purchased by the Qatari Diar investment group. 
On 14 July 1965, while walking with Marietta Tree, the then-U.S. Ambassador to the United Nations, Adlai Stevenson, suffered a heart attack, later dying at the old St George's Hospital at Hyde Park Corner. As they reached the front of the Sportsman's Club, his last words were reportedly to ask her to slow down. 
The writer Oscar Wilde lived in Grosvenor Square between 1883 and 1884,  and references to the square appear in four of his works (see section below).
Since 2003, the east of the gardens has contained a memorial garden to 67 British victims of the 11 September 2001 terrorist attacks.  The poem For Katrina's Sun-Dial by Henry van Dyke was chosen for inscription on an elliptical granite block engraved with the names of the victims, underneath which is buried a piece of the steel wreckage.
The former United States Navy building at 20 Grosvenor Square was sold in 2007 for £250 million to Richard Caring, who planned to turn it into 41 residential apartments. The Abu Dhabi Investment Council and property developer Finchatton then bought the building for the same amount in April 2013, with planning permission to convert the building into 31 luxury apartments.  
In September 2013, the Government of Canada announced its intention to sell its High Commission building at 1 Grosvenor Square and "consolidate its diplomatic activity in the UK in a single, central location in Canada House on Trafalgar Square".  
Most of the buildings on Grosvenor Square are in the Georgian style of architecture.
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Mayfair is an affluent area in the West End of London towards the eastern edge of Hyde Park, in the City of Westminster, between Oxford Street, Regent Street, Piccadilly and Park Lane. It is one of the most expensive districts in the world.
Belgravia is a district in Central London, covering parts of the areas of both the City of Westminster and the Royal Borough of Kensington and Chelsea.
Bond Street in the West End of London links Piccadilly in the south to Oxford Street in the north. Since the 18th century the street has housed many prestigious and upmarket fashion retailers. The southern section is Old Bond Street and the longer northern section New Bond Street—a distinction not generally made in everyday usage.
Grosvenor Group Limited is an internationally diversified property group, which traces its origins to 1677 and has its headquarters in London, England. It has a global reach, now in 62 international cities, with offices in 14 of them, operated on behalf of its owners, the Duke of Westminster and his family. It has four regional development and investment businesses and a portfolio of indirect investments. Its sectors include residential, office, retail, industrial, along with hotels.
The High Commission of Canada in the United Kingdom is the diplomatic mission of Canada to the United Kingdom. It is housed at Canada House on Trafalgar Square in central London, with an additional Regional Service Centre at 3 Furzeground Way in Stockley Park, Uxbridge.
Richard Seifert was a Swiss-British architect, best known for designing the Centre Point tower and Tower 42, once the tallest building in the City of London. His eponymously named practice – R. Seifert and Partners was at its most prolific in the 1960s and 1970s, responsible for many major office buildings in Central London as well as large urban regeneration projects in other major British cities.
The Embassy of the United States of America in London is the diplomatic mission of the United States in the United Kingdom. It is located in Nine Elms and is the largest American embassy in Western Europe and the focal point for events relating to the United States held in the United Kingdom.
Canada House is a Greek Revival building on Trafalgar Square in London. It has been a Grade II* Listed Building since 1970. It has served as the offices of the High Commission of Canada in the United Kingdom since 1925.
Brown Hart Gardens, located off Duke Street, Mayfair, is a 10,000 square feet (929 m2) public garden on top of an electricity substation.
Macdonald House was a seven-storey Neo-Georgian style building on Grosvenor Square in Mayfair, London. It was part of the High Commission of Canada from 1961 to 2014. Macdonald House was used for the High Commission's cultural and consular functions, trade and administrative sections, immigration section, and as the High Commissioner's official residence. From 1938 to 1960, the building was the Embassy of the United States.
Wilton Crescent is a street in central London, comprising a sweeping elegant terrace of Georgian houses and the private communal gardens that the semi-circle looks out upon. The houses were built in the early 19th century and are now Grade II listed buildings. The street is the northern projection of Belgravia and is often taken to fall into the category of London's garden squares.
The Embassy of the Republic of Indonesia in London is the diplomatic mission of Indonesia in the United Kingdom and concurrently accredited to the Republic of Ireland. From shortly after independence until the end of February 2017, the embassy was located at 38 Grosvenor Square, a leasehold building in Mayfair, close to the location of the American embassy.
The Embassy of Italy in London is the diplomatic mission of Italy in the United Kingdom. The front entrance is located on a private cul-de-sac in Mayfair, though there is also an entrance at the back on Grosvenor Square.
The Embassy of Ireland in London is the diplomatic mission of the Republic of Ireland in the United Kingdom. Ireland also maintains a Passport and Visa Office at 114A Cromwell Road, South Kensington.
In British usage, the term townhouse originally referred to the town or city residence, in practice normally in Westminster, near the seat of the monarch, of a member of the nobility or gentry, as opposed to their country seat, generally known as a country house or, colloquially, for the larger ones, stately home. The grandest of the London townhouses were stand-alone buildings, but many were terraced buildings.
Upper Grosvenor Street is a one-way Georgian street in Mayfair, London, United Kingdom. It runs from the north side of the Grosvenor House Hotel to the south side of the London Chancery Building ; both have the longest frontage of their respective streets.
South Audley Street is a major shopping street in Mayfair, London. It runs north to south from the southwest corner of Grosvenor Square to Curzon Street.
Green Street is a street in Mayfair, London. It has been built up since the mid-18th century, but most of the current properties date from the late 19th and early 20th century. It has had a number of significant residents, including various members of the British aristocracy, the James Bond author Ian Fleming, and the Beatles.
Coordinates: 51°30′41″N0°09′05″W / 51.51139°N 0.15139°W