Marble Arch is a white Carrara-marble monument at the junction of Oxford Street, Park Lane, and Edgware Road, almost directly opposite Speakers' Corner in Hyde Park in London, England. The arch is on a large traffic island, which also includes a very small park, in the midst of swirling traffic. The traffic island is directly across from the Marble Arch tube station.

The name "Marble Arch" also refers to the locality in west London where the arch is situated, particularly, the southern portion of Edgware Road. Historically, only members of the royal family and the King's Troop, Royal Horse Artillery, have been allowed to pass through the arch in ceremonial procession.

In 1828, John Nash designed the arch based on the triumphal arch of Constantine in Rome. It was originally erected on The Mall as a gateway to the new Buckingham Palace, which was rebuilt by Nash from the former Buckingham House. At that time, Buckingham Palace did not yet have its present flat east front, which meant that the inner courtyard, flanked by two wings, was still open on one side. The Marble Arch was placed at the entrance to this open side of the courtyard.

In 1851, the arch was moved to its present location during the building of the east front of the palace. (A popular story says that the arch was moved because it was too narrow for the Queen's state coach to pass through, but, in fact, the gold state coach passed under it during Elizabeth II's coronation in 1953).

It has been speculated that the arch might be moved across the street to Hyde Park, or to some other more-accessible location, instead of its current position on a large traffic island.