Knebworth House is a country house in the civil parish of Knebworth in Hertfordshire, England. It is a Grade II* listed building.
The home of the Lytton family since 1490, when Thomas Bourchier sold the reversion of the manor to Sir Robert Lytton, Knebworth House was originally a red-brick Late Gothic manor house, built round a central court as an open square. In 1813-16 the house was reduced to its west wing, which was remodelled in a Tudor Gothic style by John Biagio Rebecca for Mrs Bulwer-Lytton, and then was transformed in 1843-45 by Henry Edward Kendall Jr. into the present Tudor Gothic structure. In 1913-1914 it was leased for ₤3,000 per year by Grand Duke Michael Alexandrovich of Russia and his morganatic wife Natalia Brasova. Its most famous resident was Edward Bulwer-Lytton, the Victorian author, dramatist and statesman, who embellished the gardens in a formal Italianate fashion. Much of the interior was redesigned by Sir Edwin Lutyens, who simplified the main parterre. A herb garden, with an interlaced quincunx design, was drawn by Gertrude Jekyll in 1907, although not planted until 1982.
The current residents are Henry Lytton-Cobbold and his family. The house is open to the public together with its surrounding gardens and park. In the park is the medieval St. Mary's Church and the Lytton family mausoleum. Although it is called Knebworth House, the house and surrounding grounds are located within the borough of Stevenage.