The origins of the Three Choirs Festival lie in the relationships between the three professional cathedral choirs of Hereford, Gloucester and Worcester and their organists and assistant organists. There have been choirs of men and boys at all three cathedrals since medieval times, although each foundation has a slightly different history and structure. Records of musical collaboration before the 18th century are scanty, but the world of cathedral music was small, and it seems reasonable to assume that there was some sharing of resources and movement of personnel long before that; for example, the composer Thomas Tomkins (1572-1656) was the son of the Precentor of Gloucester Cathedral, a chorister at Gloucester himself and later organist at Worcester.
Towards the end of the 17th century music clubs linked to the cathedral choirs but focusing on performance of secular music are known to have existed in all three cities. Out of these clubs grew the music meetings, and as the repertoire became more demanding and the duration of the meetings increased, female singers were engaged to support the boy choristers. Eventually a Three Choirs Festival Chorus of amateur singers was created to perform alongside the men of the cathedral choirs in the main oratorio concerts.
This tradition continues today, with the cathedral altos, tenors and basses becoming part of the festival chorus for the evening orchestral concerts. The choristers, who now include the girl sopranos of Worcester Cathedral Girls Choir and Gloucester Cathedral Youth Choir, may sometimes take part in these concerts, often taking on the role of a semi-chorus, for example. All the choristers of the host cathedral usually take part in the festival, with smaller contingents of senior choristers from the other two.
The Three Cathedral Choirs undertake one concert on their own each year, usually accompanied by a chamber orchestra or period instrument ensemble.
Daily cathedral services of Choral Evensong sung by the three cathedral choirs are at the heart of the Three Choirs Festival week, and are attended by large congregations. One of these services is usually broadcast live by BBC Radio 3. The choirs are traditionally joined by the Three Choirs Festival Chorus and an instrumental ensemble for the Opening Service on the first Saturday morning of each festival.