Bluegrass music is a form of American roots music which has its own roots in Irish, Scottish and English traditional music. Bluegrass was inspired by the music of immigrants from the British Isles (particularly the Scots-Irish immigrants of Appalachia), as well as that of rural African-Americans, jazz, and blues. In bluegrass, as in jazz, each instrument takes a turn playing the melody and improvising around it, while the others revert to backing.

Bluegrass artists use a variety of stringed instruments to create a unique sound.Unlike mainstream country music, bluegrass relies mostly on acoustic stringed instruments. The fiddle, banjo, acoustic guitar, mandolin, and upright bass are sometimes joined by the resonator guitar (popularly known by the Dobro brand name). This instrumentation originated in rural black dance bands and was being abandoned by those groups (in favor of blues and jazz ensembles) when picked up by white musicians (van der Merwe 1989, p.62). Instrumental solos are improvised, and can frequently be technically demanding.

Since the term bluegrass came from Bill Monroe's band, The Blue Grass Boys, many consider the instruments used in his band the traditional bluegrass instruments. These were the mandolin (played by Monroe), the fiddle, guitar, banjo and upright bass. At times the musicians may perform gospel songs, singing four-part harmony and including no or sparse instrumentation (often with banjo players switching to lead guitar).

Besides instrumentation, a distinguishing characteristic of bluegrass is vocal harmony featuring two, three, or four parts, often featuring a dissonant or modal sound in the highest voice. This vocal style has been characterized as the "high lonesome sound." The "High Lonesome" sound can be credited to Shape-Note music where a high-pitched harmony, that can generally be characterized as having a nasal timbre, is sung over the main melody. There is also an emphasis on traditional songs, often with sentimental or religious themes.

Bluegrass as a style developed during the mid 1940s and is an amalgam of old-time music, blues, ragtime and jazz. Nevertheless, bluegrass's beginnings can be traced to one band. Today Bill Monroe is referred to as the "founding father" of bluegrass music; the bluegrass style was named for his band, the Blue Grass Boys, formed in 1939. The 1945 addition of banjo player Earl Scruggs, who played with a three-finger roll originally developed by Snuffy Jenkins but now almost universally known as "Scruggs style", is pointed to as the key moment in the development of this genre. Monroe's 1945-48 band, which featured banjo player Earl Scruggs, singer/guitarist Lester Flatt, fiddler Chubby Wise and bassist Howard Watts, aka "Cedric Rainwater," created the definitive sound and instrumental configuration that remains a model to this day.

It is important to note that bluegrass is not and never was folk music under a strict definition; however, the topical and narrative themes of many bluegrass songs are highly reminiscent of "folk music". In fact many songs that are widely considered to be bluegrass are older works legitimately classified as folk or old-time performed in a bluegrass style. From its earliest days to today, bluegrass has been recorded and performed by professional musicians. Although amateur bluegrass musicians and trends such as "parking lot picking" are too important to be ignored, it is professional musicians who have set the direction of the genre.

First generation bluegrass musicians dominated the genre from its beginnings in the mid-1940s through the mid-1960s. This group generally consists of those who were playing during the "Golden Age" in the 1950s, including Bill Monroe and his Blue Grass Boys, the Stanley Brothers, Lester Flatt & Earl Scruggs with the Foggy Mountain Boys, Reno and Smiley, Lonesome Pine Fiddlers, Jim & Jesse, Jimmy Martin and the Osborne Brothers, Mac Wiseman, Mac Martin and the Dixie Travelers, Carl Story and his Rambling Mountaineers, Buzz Busby, The Lilly Brothers, Jim Eanes and Earl Taylor.

Bluegrass's second generation came to prominence in the mid- to late-1960s, although many of the second generation musicians were playing (often at young ages) in first generation bands prior to this, musicians such as The Dillards, J. D. Crowe, Doyle Lawson, Sam Bush, John Hartford, Norman Blake, Frank Wakefield, Harley "Red" Allen, Bill Keith, Del McCoury and Tony Rice. With the second generation came a growth in progressive bluegrass, bands such as the The Country Gentlemen, New Grass Revival, Seldom Scene, The Kentucky Colonels. In that vein, first-generation bluegrass fiddler Vassar Clements, mandolin virtuoso David Grisman, Grateful Dead frontman Jerry Garcia (on banjo) and Peter Rowan as lead vocalist collaborated on the album Old and in the Way; the Garcia connection helped to expose progressive and traditional bluegrass to a rock music audience.

Third generation bluegrass saw a number of notable changes from the music played in previous years. In several regards, this generation saw a redefinition of "mainstream bluegrass." Increased availability of high-quality sound equipment led to each band member being miked independently, and a "wall of sound" style developed (exemplified by IIIrd Tyme Out and Lonesome River Band). Following the example set by Tony Rice, lead guitar playing became more common (and more elaborate). An electric bass became a generally, but not universally, accepted alternative to the traditional acoustic bass, though electrification of other instruments continued to meet resistance outside progressive circles. Nontraditional chord progressions also became more widely accepted. On the other hand, this generation saw a renaissance of more traditional songs, played in the newer style. The Johnson Mountain Boys were one of the decade's most popular touring groups, and played strictly traditional bluegrass.

It could be argued that a fourth generation of bluegrass musicians is beginning to appear, marked by a high level of technical skill. Although it is too soon to see definite trends, one of the most notable fourth generation musician to emerge so far is probably Chris Thile, who has recorded five solo albums since he was 13.

Since the late 1990s, several mainstream country musicians have recorded bluegrass albums. Ricky Skaggs, who began as a bluegrass musician and crossed over to mainstream country in the 1980s, returned to bluegrass in 1996, and since then has recorded several bluegrass albums and tours with his bluegrass band Kentucky Thunder. Around the same time, country music superstars Dolly Parton and Patty Loveless have both released several bluegrass albums. Along with the Coen Brothers' movie, O Brother, Where Art Thou? and the subsequent "Down From the Mountain" music tour, this has brought bluegrass music to a much wider audience. Meanwhile, bands such as the Yonder Mountain String Band in the United States, and Druhá Tráva in the Czech Republic have attracted large audiences while pushing at the edges of progressive bluegrass.

Though she is often considered a crossover or mainstream country artist, no discussion of recent developments in bluegrass music would be complete without mention of Alison Krauss. A vocalist/fiddler whose first album was released when she was just 16, Krauss and her band, Union Station, were major contributors to the soundtrack of O Brother, Where Art Thou? As a solo artist, collaborator, producer and with Union Station, Krauss has won, as of 2006, 20 Grammy Awards, the most of any female artist in history. She is now tied for 7th place on the all-time winners list.

Other notable recent bluegrass bands Cherryholmes, a family act that combines exquisite instrumental and singing talents with a style that remains reminiscent of traditional bluegrass. The Grascals, a bluegrass band that has recently formed is beginning to gain wide recognition, and Mountain Heart which was formed as a traditional bluegrass band by former members of Doyle Lawson and Quicksilver and Alison Krauss and Union Station, but has become one of the more progressive and innovative groups of the time.

www.wikipedia.org/wiki/Bluegrass_music