The International Organ Festival (IOF) is a biennial music festival and organ competition held in St Albans, England since 1963. Originally held annually, it was changed to every two years in 1965 due to the complexity of organising the increasingly ambitious programme. The festival is run mainly by volunteers.

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The festival was conceived by the organist and choirmaster of St Albans Cathedral, Peter Hurford, to celebrate the building of a new organ at the cathedral by Harrison & Harrison. The main competitions are still conducted on this instrument, its eclectic style and modern electropneumatic action now complemented by another self-contained tracker action instrument which the International Organ Festival Society, the charity which runs the Festival, has had built for its own use and sited at St Saviour's Church, St Albans. This was built by Peter Collins in the style of, and in homage to, the early 18th century German organ builder Andreas Silbermann. There is a new (2005) organ in St Peter's Church, St Albans by Mander Organs, which has played a role in the festival and competitions since 2007. Recent competitions have also visited London, with competition rounds regularly held at Christ Church Spitalfields and, in 2017, a concerto final at St John's Smith Square.

There are two main competitions, the interpretation competition and the improvisation competition (formerly known as the Tournemire Prize). Judges have included Piet Kee, Marie-Claire Alain, Anton Heiller, Ralph Downes, Harry Croft-Jackson, Thomas Trotter, Ton Koopman, Naji Hakim, Daniel Roth and David Sanger. The competition is considered prestigious, as may be judged by the list of past winners (starting with Susan Landale in 1963 and Gillian Weir in 1964), and judges have occasionally decided not to award first prize.

The Artistic Director and Executive Director since 2007 is David Titterington, professor of organ at the Royal Academy of Music.

The 2023 festival and competitions, marking the festival's 60th anniversary, took place from 3 to 15 July.

The festival's associated concert series includes large orchestral and choral works, chamber music and solo performances, as well as evening jazz. The Three Choirs concert is an audience favourite, in which over the years the choristers of St Albans Cathedral have been joined by many of England's most celebrated cathedral choirs (for instance, in 2013 Salisbury Cathedral & York Minster, in 2015 Christ Church Cathedral, Oxford and Westminster Cathedral, and in 2017 St Paul's Cathedral & Temple Church).

Many of the great orchestras (the Royal Philharmonic Orchestra, the Royal Liverpool Philharmonic Orchestra and others) have played in the Festival, and there have been recitals and concerts from performers such as John Williams, Sarah Walker, Musica Antiqua Köln, Evelyn Glennie, Emma Kirkby, James Bowman and Julian Perkins. Concerts have sometimes been broadcast on BBC Radio 3. Many concerts take place in the Cathedral, but the Festival takes place all over St Albans with other regular venues including St Peter's Church and St Saviour's Church.

The 2021 Festival was one of the first events to take place after Covid-19 restrictions were partially relaxed in the UK. Performers included Nicola Benedetti with Aurora Orchestra, Tenebrae, Jess Gillam, Steven Osborne and Roderick Williams.

The IOF Fringe presents community-focused performances in a wide range of formal and unconventional venues.

Events were mostly outdoors in historic parts of the City such as in front of the Clock Tower and in the Tudor streets of St Michael's or in the Alban Arena. Artists taking part included Seth Lakeman, The Swanvesta Social Club and Isla St Clair.

Previously, cabaret events and other entertainment had been run as part of the festival, including performances from Richard Stilgoe, Jake Thackray, Instant Sunshine and others.

The following individuals have won prizes at the festival.^[1]