Clannad (Irish pronunciation: [ˈklˠan̪ˠəd̪ˠ]) were an Irish band formed in 1970 in Gweedore, County Donegal, by siblings Ciarán, Pól and Máire (Moya) Uí Bhraonáin (in English, Brennan) and their twin uncles Noel and Pádraig Ó Dúgáin (Duggan). They have adopted various musical styles throughout their history. Beginning as an acoustic folk group mainly performing rearranged traditional Irish songs in Irish, they expanded their sound with original songs in English, vocal harmonies, electronic keyboards, and elements of rock, Celtic, new age, smooth jazz, and Gregorian chant.

Initially known as Clann as Dobhar ('Family from Dore'), they shortened their name to Clannad in 1973. By 1979 they had released three albums and toured Europe and the US. From 1980 to 1982 they operated as a six-piece with their sister and niece Eithne (Enya). In 1982, they gained international attention with their single "Theme from Harry's Game". They experimented with new age and pop-influenced sounds in the 1980s and 1990s and their music came to be defined as almost purely Celtic, making them innovators of that genre. In 1997, after 15 albums, they took a break and pursued solo projects. The band regrouped in 2007 as a four-piece with Moya (who adopted that spelling instead of Máire in 2002), Ciarán, Noel, and Pádraig and completed a world tour in 2008. In 2013, Pól rejoined and they released their first studio album in fifteen years. Pádraig Duggan died in 2016. The remaining group embarked on their farewell tour in 2020 as a quartet.

Clannad have won numerous awards throughout their career, including a Grammy Award, a BAFTA, an Ivor Novello Award, and a Billboard Music Award. They have recorded in six different languages and scored eight UK top 10 albums. They were often more popular abroad than in their native Ireland, and are considered to have brought Irish music and the Irish language to a wider audience.

Clannad was formed by siblings Ciarán, Máire, and Pól Brennan with their twin uncles Noel and Pádraig Duggan. They grew up in Dore, a remote parish in Gweedore, County Donegal; in north-western Ireland, it is a Gaeltacht region where Irish is the main spoken language. They were raised as a Roman Catholic family of musicians: the Brennans' mother, Máire "Baba" Brennan (née Duggan), the daughter of the local headmaster, was a music teacher and later choir leader; and their father, Leo Brennan, who played saxophone and accordion, was a member of the Slieve Foy, an Irish showband that had toured Ireland and Scotland. In 1968, the Brennan and Duggan fathers bought and restored a dilapidated old tavern in nearby Meenaleck and ran it as a music bar called Leo's Tavern. Their children performed there together and developed their own act, with Ciaran and Pól Brennan on bass, vocals, and bongos; Pádraig and Noel Duggan on guitars; and elder Brennan sister Máire on harp and vocals.

The five young musicians made their live debut in 1970 at a music competition held during the inaugural Slógadh Youth Festival in Letterkenny. Máire, the eldest member, who had learned the harp and could play "holy songs and Brian Boru", was elected lead vocalist. They had not intended to enter the competition, but were encouraged to try by the local police sergeant and family members, and they submitted their entry form with ten minutes to spare before the post was to be collected. They won the Slógadh competition prize of Ir£500, a trophy, and a recording contract with Polydor Records, although the band members were too young to sign it. With help from a grandfather, they had named themselves Clann as Dobhar, Irish for 'Family from Dore', and they used this name until 1973, when they shortened the name to Clannad.

They established themselves as an acoustic folk group, collecting material from old singers and story-tellers in Donegal and building a repertoire of traditional Irish songs, arranged in a contemporary style for a full band. This approach attracted criticism at first because the Irish language was associated with poverty, but as Pól Brennan recalled: "Once they said that ... we just had to do it even more." They also wrote original material, and covered songs by the Beatles, the Rolling Stones, and Joni Mitchell.

In 1973, Clannad came in first place in the Letterkenny folk festival and were offered a deal with Philips Records, which they negotiated themselves. Having secured a label, the group prepared material for a debut album. They recorded at Eamonn Andrews Studios in Dublin, choosing Irish- and English-language songs and a cover of "Morning Dew" by Bonnie Dobson. Released in 1973, Clannad was met with initial resistance from the label because of the use of Irish, and the group soon found themselves more popular outside Ireland, particularly in Germany. Later in 1973, Clannad competed for Ireland in the heat stages of the 1973 Eurovision Song Contest with the song "An Pháirc".

In 1974, the band followed their debut album with Clannad 2, released by Gael Linn Records and produced by Dónal Lunny, the founder of Planxty and the Bothy Band. Like their first album, Clannad 2 featured a mixture of English- and Irish-language songs, with Lunny and members of the Bothy Band on additional instruments. It also featured the band's first use of a synthesizer, and was heavier on the folk-rock side, with notable electric guitar, that several later releases.