Bluegrass has roots in traditional North European music, such as Irish ballads and dance tunes, as well as African American genres like blues and jazz.

[3] It was further developed by musicians who played with Monroe, including 5-string banjo player Earl Scruggs and guitarist Lester Flatt.

[3] In bluegrass, as in most forms of jazz, one or more instrumentalists take a turn playing the melody and improvising around it, while the others perform accompaniment; this is especially typified in tunes called breakdowns.

[5] This is in contrast to old-time music, where all instrumentalists play the melody together, or one instrument carries the lead throughout while the others provide accompaniment.

Traditional bluegrass performers believe the "correct" instrumentation is that used by Bill Monroe's band, the Blue Grass Boys (guitar, mandolin, fiddle, banjo, and bass).

Alison Krauss and Union Station provide a good example of a different harmony stack with a baritone and tenor with a high lead, an octave above the standard melody line, sung by the female vocalist.

However, by employing variants to the standard trio vocal arrangement, they were simply following a pattern existing since the early days of the genre.

[18] Mandolin player Pee Wee Lambert sang the high baritone above Ralph Stanley's tenor, both parts above Carter's lead vocal.

[19] This trio vocal arrangement was variously used by other groups as well; even Bill Monroe employed it in his 1950 recording of "When the Golden Leaves Begin to Fall".

Aside from laments about loves lost, interpersonal tensions and unwanted changes to the region (e.g., the visible effects of mountaintop coal mining), bluegrass vocals frequently reference the hardscrabble existence of living in Appalachia and other rural areas with modest financial resources.

[24] Much later, in 1945, Earl Scruggs would develop a three-finger roll on the instrument which allowed a rapid-fire cascade of notes that could keep up with the driving tempo of the new bluegrass sound.

[25] These traditions consisted primarily of English and Scottish ballads—which were essentially unaccompanied narrative—and dance music, such as reels, which were accompanied by a fiddle.

Radio stations dedicated to bluegrass have also proved influential in advancing the evolution of the style into distinctive subgenres.

In 1948, the Stanley Brothers recorded the traditional song "Molly and Tenbrooks" in the Blue Grass Boys' style, arguably the point in time that bluegrass emerged as a distinct musical form.

[36] Monroe's 1946 to 1948 band, which featured guitarist Lester Flatt, banjoist Earl Scruggs, fiddler Chubby Wise and bassist Howard Watts (also known as "Cedric Rainwater") – sometimes called "the original bluegrass band" – created the definitive sound and instrumental configuration that remains a model to this day.

In 1967, the banjo instrumental "Foggy Mountain Breakdown" by Flatt and Scruggs was introduced to a worldwide audience as a result of its frequent use in the movie "Bonnie and Clyde".

But the functionally similar old-time music genre was long-established and widely recorded in the period of the film's events and later CD was released.

It was decided that since Bill was the oldest man, and was from the bluegrass state of Kentucky and he had the Blue Grass Boys, it would be called 'bluegrass.

In most traditional bluegrass bands, the guitar rarely takes the lead, instead acting as a rhythm instrument, one notable exception being gospel-based songs.

Due to the exposure traditional bluegrass received alongside mainstream country music on radio and televised programs such as the Grand Ole Opry, a wave of young and not exclusively Southern musicians began replicating the genre's format on college campuses and in coffeehouses amidst the American folk music revival of the early 1960s.

New Grass Revival began utilizing electric instrumentation alongside songs imported from other genres to great popularity in the 1970s and 1980s, and the term "newgrass" became synonymous with "progressive bluegrass".

Following the death of Jerry Garcia, who began his career playing bluegrass, and the dissolution of the Grateful Dead, the blossoming "jam band" scene that followed in their wake embraced and included many groups that performed progressive bluegrass styles that included extended, exploratory musical improvisation, often called "jamgrass."

[41][42][43] In 2012, the critically acclaimed Dutch-language Belgian film, The Broken Circle Breakdown, featured Flemish musicians performing Bluegrass music central to the story.

[44][45] International bluegrass groups include Hayde Bluegrass Orchestra and Ila Auto from Norway; Rautakoura and Steve 'n' Seagulls from Finland; Druhá Tráva and Poutníci from the Czech Republic (home of the subgenre, Czech bluegrass); Hutong Yellow Weasels and The Randy Abel Stable from China; Heartbreak Hill and Foggy Hogtown Boys from Canada; the U.K.'s The Beef Seeds, Southern Tenant Folk Union, and Police Dog Hogan; and Australia's Flying Emus, Mustered Courage, and Rank Strangers.