Marty Stuart began collaborating with legends when he joined Lester Flatt's Nashville Grass as a 13-year-old mandolinist. One of his biggest singles, 1991's "The Whiskey Ain't Workin'," teamed him with Travis Tritt. This compilation includes a rare Stuart mandolin workout on Bill Monroe's "Rawhide" recorded onstage with Flatt in 1974, and "Hearts Like Ours" with wife Connie Smith. He and ex-father-in-law Johnny Cash created a fiery revival of Cash's Sun recording of "Doin' My Time." With Steve Earle, Stuart created a beautifully understated rendition of Buddy Holly's "Crying, Waiting, Hoping." He was equally adept with Earl Scruggs on "John Henry" and with Merle Haggard on a 2003 "Farmer's Blues." That empathy extended to blues and gospel greats, apparent on "The Weight" with the Staple Singers and "Confessin' the Blues" with B.B. King. Two unreleased tracks include Stuart and Loretta Lynn reviving "Will You Visit Me on Sunday," a tune she'd previously recorded with the late Conway Twitty, and the Who's "I Can See for Miles" with Stuart, his band, and Old Crow Medicine Show. Unlike the many Nashville "vocal events" that are simply contrived marketing ploys, Stuart's collaborations are consistently organic, without a shred of artifice. --Rich Kienzle