Smithfield, properly known as West Smithfield, is a district located in Central London, part of Farringdon Without, the most westerly ward of the City of London, England.

Smithfield is home to a number of City institutions, such as St Bartholomew's Hospital and livery halls, including those of the Butchers' and Haberdashers' Companies. The area is best known for the Smithfield meat market, which dates from the 10th century, has been in continuous operation since medieval times, and is now London's only remaining wholesale market. Smithfield's principal street is called West Smithfield. Each summer, from the 12th century to the 19th century the area hosted Bartholomew Fair, and the area also contains the City's oldest surviving church building, St Bartholomew-the-Great, dating from 1123 (most City churches were destroyed in the Great Fire of 1666).

The area is located just beyond the New Gate and formerly its prison which held condemned prisoners. In former centuries, especially prior to the establishment of Tyburn, the area bore witness to many executions of heretics and political rebels, as well as Scottish knight Sir William Wallace, and Wat Tyler, leader of the Peasants' Revolt, among many other religious reformers and dissenters (later on, public executions were generally moved out to Tyburn, until being moved back to the prison).

The present Smithfield Market, a Grade II listed-covered market building, was designed by Victorian architect Sir Horace Jones in the second half of the 19th century, and is the dominant architectural feature of the area. Some of its original market premises fell into disuse in the late 20th century and faced the prospect of demolition. The Corporation of London's public enquiry in 2012 drew widespread support for an urban regeneration plan intent upon preserving Smithfield's historical identity.

In the Middle Ages, it was a broad grassy area known as Smooth Field, located beyond London Wall stretching to the eastern bank of the River Fleet. Given its ease of access to grazing and water, Smithfield established itself as London's livestock market, remaining so for almost 1,000 years. Many local toponyms are associated with the livestock trade: while some street names (such as "Cow Cross Street" and "Cock Lane") remain in use, many more (such as "Chick Lane", "Duck Lane", "Cow Lane", "Pheasant Court", "Goose Alley") have disappeared from the map after the major redevelopment of the area in the Victorian era.

In 1123, the area near Aldersgate was granted by King Henry I for the foundation of St Bartholomew's Priory at the request of Prior Rahere, in thanks for his being nursed back to good health. The Priory exercised its right to enclose land between the vicinity of the boundary with Aldersgate Without (to the east), Long Lane (to the north) and modern-day Newgate Street (to the south), erecting its main western gate which opened onto Smithfield, and a postern on Long Lane. By facing the open space of Smithfield and by having 'its back to' the buildings lining Aldersgate Street, the Priory site has left a continuing legacy of limited connectivity between the Smithfield area and Aldersgate Street.

The Priory thereafter held the manorial rights to hold weekly fairs, which initially took place in its outer court on the site of present-day Cloth Fair, leading to "Fair Gate".

An additional annual celebration, the Bartholomew Fair, was established in 1133 by the Augustinian canons. Over time, this became one of London's pre-eminent summer fairs, opening each year on 24 August. A trading event for cloth and other goods as well as being a pleasure forum, the four-day festival drew crowds from all strata of English society.