St. James's Square is the only square in the exclusive St James's district of the City of Westminster. It has predominantly Georgian and neo-Georgian architecture and a private garden in the centre. For its first two hundred or so years it was one of the three or four most fashionable residential address in London. It is now home to the headquarters of a number of well-known businesses, including BP and Rio Tinto Group; to two London gentlemen's clubs, the East India Club and the Naval and Military Club; and to the London Library. Also based in the square is the world-famous think-tank the Royal Institute for International Affairs, better known as Chatham House.