Longleat is a stately home about 4 miles (7 km) west of Warminster in Wiltshire, England. A leading and early example of the Elizabethan prodigy house, it is a Grade I listed building and the seat of the Marquesses of Bath.

Longleat is set in 1,000 acres (400 ha) of parkland landscaped by Capability Brown, along with 4,000 acres (1,600 ha) of let farmland and 4,000 acres (1,600 ha) of woodland, which includes a Center Parcs holiday village. It was the first stately home to open to the public, and the Longleat estate has the first safari park outside Africa and other attractions including a hedge maze.

The house was built by Sir John Thynne and designed mainly by Robert Smythson, after Longleat Priory was destroyed by fire in 1567. It took 12 years to complete and is widely regarded as one of the finest examples of Elizabethan architecture in Britain. It continues to be the seat of the Thynn family, who have held the title of Marquess of Bath since 1789; the eighth and present Marquess is Ceawlin Thynn.

Longleat was previously an Augustinian priory. The name comes from "leat", an artificial waterway or channel such as that which supplies a watermill.

Sir Charles Appleton (1515–1580) purchased Longleat for Sir John Thynn in 1541 for £53. Appleton was a builder with experience gained from working on The Old School Baltonsborough, Bedwyn Broil and Somerset House. In April 1567 the original house caught fire and burnt down. A replacement house was effectively completed by 1580. Adrian Gaunt, Alan Maynard, Robert Smythson, the Earl of Hertford and Humpfrey Lovell all contributed to the new building but most of the design was Sir John's work. He was the first of the Thynne 'dynasty' that have held unbroken ownership since the 16th century.

Sir John's immediate descendants were Sir John Thynne the Younger (1555–1604) and then Sir Thomas Thynne (ca. 1578–1639). Thomas's secret marriage to his family's enemy is said to have inspired Shakespeare's Romeo and Juliet; Sir James Thynne (1605–1670) employed Sir Christopher Wren to carry out modifications to the house; and was succeeded by Thomas Thynne (1646–1682), and then Thomas Thynne, 1st Viscount Weymouth (1640–1714) who started the house's large book collection. Formal gardens, canals, fountains and parterres were created by George London with sculptures by Arnold Quellin and Chevalier David. The Best Gallery, Long Gallery, Old Library and Chapel were all added by Christopher Wren.

Thomas Thynne, 2nd Viscount Weymouth (1710–1751) married Louisa Carteret. Thomas Thynne, 1st Marquess of Bath (1734–1796) employed Capability Brown who replaced the formal gardens with a landscaped park and dramatic drives and entrance roads. Thomas Thynne, 2nd Marquess of Bath (1765–1837) employed Jeffry Wyatville to modernise the house and received advice from Humphrey Repton on the grounds. Wyatville demolished several parts of the house, including Wren's staircase, and replaced them with galleries and a grand staircase. He also constructed many outbuildings including the Orangery. Henry Thynne, 3rd Marquess of Bath (1797–1837) was succeeded by John Thynne, 4th Marquess of Bath (1831–1896) who collected Italian fine arts. He employed John Crace, whose prior work included Brighton Pavilion, Woburn Abbey, Chatsworth House and the Palace of Westminster, to add Italian renaissance style interiors. Thomas Thynne, 5th Marquess of Bath (1862–1946) inherited in 1896. During World War I, the house was used as a temporary hospital. During World War II, it became the evacuated Royal School for Daughters of Officers of the Army. An American hospital was also constructed in the grounds; Henry Thynne, 6th Marquess of Bath (1905–1992) inherited in 1946. Faced with considerable death duties he sold large parts of the wider estates; to allow Longleat itself to survive, he opened the house to public visitors. Russell Page redesigned the gardens around the house to allow for tourists. The safari park opened in 1966. Alexander Thynn, 7th Marquess of Bath (1932–2020) was an artist and mural painter with a penchant for mazes and labyrinths: he created the hedge maze, the love labyrinth, the sun maze, the lunar labyrinth and King Arthur's maze on the property. Ceawlin Thynn, 8th Marquess of Bath (born 1974) inherited in 2020.

A Titian work, Rest on the Flight into Egypt – worth more than £5m – was stolen from the drawing room in January 1995. It was found in a plastic shopping bag in London in 2002. Longleat staged the Red Bull Air Race in 2005. A copy of the painting The Fallen Madonna, a running joke from the BBC television sitcom 'Allo 'Allo!, was made for Henry Thynne and hangs in Longleat House.