One of Ireland's foremost traditional groups, Altan emerged in the early '90s with a sound that heavily featured the Irish-language songs and dynamic twin-fiddling style of their native Donegal and brought it to the world stage via a string of successful releases, first for the Celtic-oriented Green Linnet label, and later on Virgin, Narada, and Compass Records. Employing fiddle, flute, guitars, accordion, bouzouki, and the lilting bilingual vocals of Mairéad Ní Mhaonaigh, Altan built and maintained a global audience through decades of widespread touring and recorded highlights like 1993's Island Angel, 2002's The Blue Idol, and 2015's exploratory Celtic-American fusion album, The Widening Gyre. In spite of their various collaborations and experiments outside their core genre, Altan have remained steadfastly devoted to the traditional music of Ireland with frequent emphasis on their native Northern Irish region of Donegal. They began with the partnership of Donegal-born fiddler and vocalist Mairéad Ní Mhaonaigh and Belfast-born flute and whistle player Frankie Kennedy. Irish-speaking Mhaonaigh's youth had been steeped in traditional music and she initially learned to play the fiddle from her father, Francie, who in turn had learned it from his mother, Roise. Influential Irish fiddler Dinny McLaughlin, who frequented her childhood home, also added to her knowledge of the instrument. Kennedy, who had grown up studying the flute, was extremely interested in Irish music and would make trips to Donegal to immerse himself in traditional sessions. After meeting during an informal jam session, Ní Mhaonaigh and Kennedy began to play together at every opportunity. Although they both took jobs as trainee teachers at St. Patrick's College in Dublin, performing music remained their shared passion. In 1979, the two musicians made their recording debut as accompanists for Gaelic singer Albert Fry on his self-titled debut album. Two years later, Ní Mhaonaigh and Kennedy both graduated from college and were married. Together with bouzouki player Donal O'Hanlan and Mairéad's brother Gearóid Ó Maoinaigh, who played guitar, Ní Mhaonaigh and Kennedy formed a band, Ragaime. Although they recorded for RTE, the group disbanded by the time that Gael-Linn released Ní Mhaonaigh and Kennedy's debut album as a duo, Ceol Aduaidh, in December 1983.

In 1987, Ní Mhaonaigh and Kennedy recorded their second album as a duo which they named Altan, after a lake in northwest Donegal. Produced by Dónal Lunny, the album began their longtime partnership with Green Linnet Records and featured accompaniment by Ciarán Curran on bouzouki, Mark Kelly on guitar, and Mairéad's sister Anna Ní Mhaonaigh, then a member of the all-woman group Macella. Shortly after its release, the musicians agreed to continuing working together and adopted the album's title as their name. During the summer of 1988, Altan began work on their first album as a band, which now included Paul O'Shaughnessy on twin fiddle. Produced by Phil Cunningham and released in 1989, Horse with a Heart featured a more dynamic sound than its predecessors. As the band's touring schedule expanded, O'Shaughnessy and Kelly were forced by their day jobs to restrict their activity with Altan to recordings and performances closer to home. During the band's U.S. tours, their places were taken by Daíthí Sproule on guitar and Ciarán Tourish on fiddle. Altan's success became more widespread with their 1990 album Red Crow, which received a NAIRD award as Best Celtic Traditional Album, an honor that was also extended to their next album, 1992's Harvest Storm. That same year, Kennedy was diagnosed with Ewing's Sarcoma, a type of bone cancer. While undergoing treatment, he continued to maintain his post in the band and was a key part of Altan's 1994 career highlight, Island Angel, which according to Billboard proved to be one of the top-selling world music albums of the year. Even as his health was failing, Kennedy performed with Altan at the invitation of President Bill Clinton at the White House, and helped them orchestrate a major-label contract with Virgin Records shortly before his death on September 19, 1994.

Honoring their fallen bandmate's wishes that they carry on, accordionist Dermot Byrne, a former guest collaborator, was invited to join Altan full-time and appeared on their 1996 Virgin debut Blackwater. The lineup at this point had solidified to include Tourish accompanying singer Ní Mhaonaigh on fiddle, Curran on bouzouki, Kelly and Sproule on guitar, and newcomer Byrne on accordion and would stay that way for nearly two decades. Following 1997's Runaway Sunday, Altan switched to the Narada label and began the next decade with 2000's Another Sky, which deviated a bit from their almost entirely Irish formula by including both a Bob Dylan cover ("Girl from the North Country") and the Scots-language adaptation of Robert Burns' "Green Grow the Rushes." This tendency toward genre cross-pollination continued on 2002's The Blue Idol, which featured an appearance by American country icon Dolly Parton. Following 2005's more traditionally Irish Local Ground, Altan went on a hiatus during which several members worked on solo releases, including Ní Mhaonaigh on her 2009 album Imeall.

In early 2009 Altan returned to the studio to re-record a collection of highlights from their catalog accompanied by Dublin's famed RTÉ Concert Orchestra. The resulting album, 25th Anniversary Collection, was released in January 2010 and in addition to honoring their first quarter century together, marked their first outing for the Compass label. The group spent the remainder of the year touring Ireland, Europe, and the U.S. in celebration of their anniversary year. Altan's next studio album, 2012's Gleann Nimhe: The Poison Glen, proved to be somewhat of a back-to-basics release, eschewing the orchestral grandeur of their previous project as well as the occasional synths and new age elements that had characterized some of their work in the decade prior. In early 2014, the group's long-held lineup shifted with the departure of accordionist Dermot Byrne. Martin Tourish stepped up as his replacement and was a full-time member for their next project, 2015's The Widening Gyre. A fusion of Altan's traditional Irish fare and American roots music, the album featured a host of guests including Mary Chapin Carpenter, Darol Anger, Alison Brown, Sam Bush, and many others. Several more years of touring followed and in 2017, the core lineup shifted again with the departure of longtime fiddler Ciarán Tourish. Returning to Donegal's Attica Studios, Altan recorded their 12th studio album, The Gap of Dreams, released in 2018.~ Craig Harris, Rovi