This four-disc, 87-track retrospective covers the first four decades of one of the most successful "folk" labels in history. Co-founders/owners Ken Irwin, Marian Leighton Levy, and Bill Nowlin assembled a collection that showcases -- one disc per decade -- how deeply entrenched the label was in the 1970s in exposing various forms of folk music from traditional to emergent ones, and how its focus expanded. Disc one includes tracks by newgrass outfit J.D. Crowe & the New South, outsider songwriter Michael Hurley, banjoist Ola Belle Reed, Appalachian traditionalists Hazel Dickens and Alice Gerrard, and ace superpicker Norman Blake and the Cajun sounds of D.L Menard & the Louisiana Aces. It also reveals the label's first big directional shakeup by including George Thorogood & the Delaware Destroyers' scorching read of Bo Diddley's "Who Do You Love." The '80s reflect a wider reach still, with tracks by soulman Ted Hawkins, the Klezmer Conservatory Band, polka revisionists Brave Combo, country songwriter Keith Whitley, and blues artists Rory Block and Johnny Copeland. There's also a deeper step into Louisiana traditions with music by Professor Longhair, James Booker, and Buckwheat Zydeco included, too. This decade also signaled the arrival of Nanci Griffith on Rounder's Philo imprint. In the '90s, Rounder's profile was enhanced by the arrival of bluegrass queen Alison Krauss, who has been a best-selling artist for them ever since. There were more singer/songwriter types on the imprint too, such as Bill Morrissey, Tish Hinojosa, and Jimmie Dale Gilmore; more modern electric blues and R&B talents were showcased too in Marcia Ball, Irma Thomas, Tracy Nelson, Ruth Brown, Johnny Adams, and Wilson Pickett; and the label still held traditional sway with bluegrass mainstay Krauss and uber-tradtionalist James King. The first decade of the new century reveals Rounder's wide range in embracing everything they felt they could sell: from Americana-drenched rock acts such as Son Volt and the Cowboy Junkies to uber-rockers Rush; the vanguard pop of They Might Be Giants and jazzy chanteuse Madeleine Peyroux; to British folk maven Linda Thompson, as well as experimental projects like the Grammy-winning Raising Sand by Robert Plant and Krauss. Country-pop legend and stalwart Willie Nelson also recorded for them. But no matter their genre extensions, bluegrass is still part of Rounder's mix, as cuts by Dailey & Vincent, Rhonda Vincent, and Blue Highway attest. It's impressive to be sure. That said, despite the range of music here and the fine historical essay by Geoffrey Himes, two chapters are missing: a disc that focuses on their vast licensing of traditional music, and the essential collection of tracks by American songwriting icons such as Tom Russell, Ray Wylie Hubbard, Guy Clark, rockabilly queen Rosie Flores, and R&B legend Eddie Hinton, most of whom recorded multiple albums for the label and its subsidiaries. Here's hoping Rounder will consider a second collection to showcase these lesser-selling projects from essential artists who are an indelible part of its story.