Fortnum & Mason plc (colloquially often shortened to just Fortnum's) is an upmarket department store in London, England. The main store is located at 181 Piccadilly in the St James's area of London, where it was established in 1707 by William Fortnum and Hugh Mason. There are additional stores at The Royal Exchange, St Pancras railway station, Canary Wharf and Heathrow Airport in Greater London, at Victoria Dockside in Hong Kong, as well as various stockists worldwide. Fortnum & Mason has been privately owned by Wittington Investments Limited since 1951.

Founded as a grocery store, Fortnum's reputation was built on supplying high quality food, and it saw rapid growth throughout the Victorian era. Although Fortnum's developed into a department store, it continues to focus on stocking a variety of exotic and specialty food along with 'basic' provisions. It is known for its food hampers. The main store has since opened several other departments, such as the gentlemen's department on the first floor. It also contains a tea shop and several restaurants.

William Fortnum was a footman in the household of Queen Anne. The royal family's insistence on having new candles every night resulted in large amounts of half-used wax, which Fortnum promptly resold. Fortnum also had a side business as a grocer. He convinced his landlord, Hugh Mason, to be his associate, and they founded the first Fortnum & Mason store in Mason's small shop at St James's Market in 1707. In 1761, William Fortnum's grandson Charles went into the service of Queen Charlotte, and the connection with the royal court led to an increase in business. Fortnum & Mason claims to have invented the Scotch egg, in 1738. The store began to stock speciality items, namely ready-to-eat luxury meals such as poultry or game served in aspic jelly.

During the Napoleonic Wars, the emporium supplied dried fruit, spices and other preserves to British officers. In the Victorian era, it was frequently called upon to provide food for prestigious court functions. Queen Victoria sent shipments of Fortnum & Mason's concentrated beef tea to Florence Nightingale's hospitals during the Crimean War.

Charles Drury Edward Fortnum (1820–1899), of the family, was a distinguished art collector and a Trustee of the British Museum, to which he donated his collection of Islamic ceramics.

In 1886, after having bought the entire stock of five cases of a new product made by H. J. Heinz, Fortnum & Mason became the first store in Britain to stock tins of baked beans.

The shop at 181–184 Piccadilly was rebuilt between 1926 and 1927 to a Neo-Georgian design by the architects Wimperis, Simpson and Guthrie. The building also incorporates 22–27 Duke Street and 42–45 Jermyn Street.

In April 1951, the Canadian businessman W. Garfield Weston acquired the store and became its chairman following a boardroom coup. In 1964, he commissioned a four-ton clock to be installed above the main entrance of the store as a tribute to its founders. Every hour, 4-foot-high (1.2 m) models of William Fortnum and Hugh Mason emerge and bow to each other, with chimes and 18th-century style music playing in the background. The chimes were incorporated into Jonathan Dove's orchestral adaptation of Zeb Soanes' children's book Gaspard's Foxtrot, which depicts the clock and its figures as illustrated by James Mayhew. Since Garfield Weston's death in 1978, the store has been run by two of his granddaughters, Jana Khayat and Kate Hobhouse. The Chief Executive Officer is Tom Athron, who joined the business in December 2020.