Glyndebourne Festival Opera is an annual opera festival held at Glyndebourne, an English country house near Lewes, in East Sussex, England.

Under the supervision of the Christie family, the festival has been held annually since 1934, except in 1941–45 during World War II and 1993 when the theatre was being rebuilt, for a 1994 reopening. Gus Christie, son of Sir George Christie and grandson of festival founder John Christie, became festival chairman in 2000.

Since the company's inception, Glyndebourne has been particularly celebrated for its productions of Mozart operas. Recordings of Glyndebourne's past historic Mozart productions have been reissued. Other notable productions included their 1980s production of George Gershwin's Porgy and Bess, directed by Trevor Nunn, and later expanded from the Glyndebourne stage and videotaped in 1993 for television, with Nunn again directing. While Mozart operas have continued to be the mainstay of its repertory, the company has expanded it with productions of Janáček and Handel operas.

Glyndebourne has two resident orchestras – the London Philharmonic Orchestra (since 1964) and the Orchestra of the Age of Enlightenment. In January 2014, Robin Ticciati became the seventh music director of the company.

Past general directors of the festival have included David Pickard. In November 2015, the festival announced the appointment of Sebastian F. Schwarz as its general director, effective in May 2016. In March 2018 Schwarz stepped down as general director. In August 2018, the festival announced the appointment of Stephen Langridge as its next artistic director, effective in the spring of 2019.

The festival operates without subsidy. Its first placement of advertisements was in 2003. The festival has planned to incorporate power by wind turbine, as part of its "green" initiatives.

Many Glyndebourne attendees come from London, and the event is regarded as part of the English summer season. Performances start in the afternoon, enabling Londoners to leave town after lunch, and finish in time for them to catch the last train back. A long interval allows opera-goers the opportunity for picnic dinners on the extensive lawns or in one of the restaurants in the grounds. Annually in London, the company presents an opera performance at The Proms.

In 1968, Glyndebourne Festival Opera established a touring ensemble, Glyndebourne Touring Opera, which in its first season took opera productions to Newcastle, Liverpool, Manchester, Sheffield and Oxford. In addition to bringing the work of Glyndebourne Festival Opera to audiences some distance from Glyndebourne, Glyndebourne Touring Opera offers opportunities for younger opera singers to develop their craft. In 2003, the Glyndebourne Touring Opera administrative duties were absorbed back into the main Glyndebourne Festival Opera administration, and the touring company was renamed Glyndebourne on Tour. The touring company now has the name of Glyndebourne Tour. Unlike Glyndebourne Festival Opera, Glyndebourne Tour does receive some subsidy, from the Arts Council England.