Manor Farm is a 22-acre (8.9 ha) historic site in Ruislip, Greater London. It incorporates a medieval farm complex, with a main old barn dating from the 13th century and a farm house from the 16th. Nearby are the remains of a motte-and-bailey castle believed to date from shortly after the Norman conquest of England. Original groundwork on the site has been dated to the 9th century.

Ownership of the site passed to the King's College, Cambridge in the 15th century. The Great Barn and Little Barn were recognised by a member of the Royal Society of Arts in 1930 as in need of conservation, and in 1931 Manor Farm was included in the sale of Park Wood as a gift to the people of Ruislip. The site continued as a working farm until 1933, and is now run as a community resource by the London Borough of Hillingdon.

Throughout 2007 and 2008, the site was restored with funding from the National Lottery, and has become a heritage area for the London Borough of Hillingdon. Manor Farm is within the Ruislip Village Conservation Area. Events are regularly held within the 13th-century Great Barn and around the rest of the site.

What remains of the motte-and-bailey castle can be seen today in part of the moat and bank on the site. Today, the moat on the site is a scheduled monument, believed to have been extended to create an oval area upon which a wooden castle covering 350 feet (110 m) by 200 feet (61 m) was built, presumably for the landowner, Ernulf de Hesdin. He was given control of the manor of Ruislip shortly after the Norman conquest, in recognition of his loyalty to William the Conqueror. The castle is believed to have been built between 1066 and 1087, but does not appear in the 1086 Domesday Book and so could have been demolished or changed significantly. It may never have been finished.

Ruislip parish was owned by the Benedictine Bec Abbey of Normandy between 1096 and 1404 during which time the prior built a home for himself on the site, surrounded by a moat. During the 16th century, the remains of the motte-and-bailey site were used as the gardens of the Manor Farm House when it was built. In 1888 the moat extension was filled in by Henry James Ewer, who farmed on the site. The moat's shape and the presence of traces of a fortified building have allowed this part of the site to be dated to the 11th century. However, the castle is believed to have been built around 1066 then either demolished or changed significantly as it does not appear as a castle in Domesday Book.

The farm buildings date back to the 13th century with the Great Barn the most prominent. The barn is the second largest such structure in Middlesex after another in Harmondsworth. The Great Barn is constructed of English oak from the nearby Ruislip Woods. It was built to a design known as an aisled barn, whereby smaller out-shoots run alongside the main supports underneath one main roof.

Studies by English Heritage have found that the site originally functioned not only as the manorial court hall for Ruislip, but also as a working farm. The main building was built over two existing structures, possibly to accommodate the new lessee of the manor, Robert Drury (1456-1536), a former Speaker of the House of Commons. The study concluded this was most likely achieved by a team of masons and carpenters. Manor Farm was also known as Ruislip Court until the 19th century.

In 1451, ownership of the farm passed with the rest of Ruislip to King's College, Cambridge who remain titular Lords of the Manor. King's completed two surveys of the manor during their ownership, in 1565 and 1750.