Here's an intro to bluegrass with a focus on its current directions. First off, here's a bit from Wikipedia:
"Bluegrass music is a form of American roots music. It 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 in 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; this is in contrast to old-time music, in which all instruments play the melody together or one instrument carries the lead throughout while the others provide accompaniment. Bluegrass is distinctively acoustic, rarely using electrical instruments.
Bluegrass as a style developed during the mid 1940s. Because of war rationing, recording was limited during that time, and the best that can be said is that bluegrass was played some time after World War II, but no earlier. As with any musical genre, no one person can claim to have "invented" it. Rather, bluegrass 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 considered the key moment in the development of this genre. Monroe's 1945 to 1948 band, which featured Scruggs, singer-guitarist Lester Flatt, fiddler Chubby Wise and bassist Howard Watts, also known as "Cedric Rainwater," created the definitive sound and instrumental configuration that remains a model to this day."
I've got a link to Lester Flatt and Earl Scruggs who were just mentioned at the end of this link. I put it at the end because, despite the fact that it's great music, if you've ever heard of bluegrass at all, you are likely already thinking of their style. Their likely most famous number is the theme song to the Beverly Hillbillies, so you already know that.
Bluegrass has been going though a number of innovations in the last couple decades. Some of the people most pushing the possibilities of bluegrass include Bela Fleck, Sam Bush, Jerry Douglas, and Edgar Meyers, who all got together for a sort of supergroup in the 80s called Strength in Numbers. Here's a beautiful song called Winter's Night
Another direction that bluegrass took in the late 90s can be personified by Alison Krauss and Union Station. They do a number of traditional style bluegrass tunes. They also do many songs where Alison's voice is the feature and the band supports her. Here's a number that let's you see a little of both.
Bluegrass became popular enough in the mid-90s that a lot of country stars who grew up with the stuff turned back to it. Dolly Parton in particular made a number of top quality albums in the bluegrass style. Many people had sort of forgotten how good of a singer and songwriter she is behind her legendary personality. Here she is doing a great and depressing song called Mountain Angel that she wrote.
One of the other great trends in the last 10 years is the emergence of bands who grew up on bluegrass as well as rock like everyone else. A lot of bluegrass bands in this set are jam bands as well. Two very popular groups are Nickel Creek and Yonder Mountain String Band. The Nickel Creek video is nice because it adds a bit of history, too.
Yonder Mountain String Band
As you can see bluegrass is very much alive and growing. Another piece of evidence is this band of kids, Pacific Ocean Bluegrass playing with guest on fiddle Katie Nakamura.
So there's a taste of the future of bluegrass. To go way back in time now, here are Flatt and Scruggs
And if it's hard to see any connection between this stuff and Scotch-Irish folk music, as Wikipedia claimed, here we have Earl Scruggs on banjo with The Chieftains. He fits right in.