Smith included material released as late as 1940, with a selection of union songs making their first appearances for an Anthology set.

Writing for Allmusic, critic Richie Unterberger wrote of the album "It does differ from the first three volumes in its focus on a slightly later period, with all the tracks culled from the years 1928–1940.

Lead Belly, Robert Johnson, Joe Williams, Bukka White, Memphis Minnie, and John Estes are all major blues artists; the Monroe Brothers, the Carter Family, Uncle Dave Macon, and the Blue Sky Boys all giant country/bluegrass pioneers; and the Hackberry Ramblers are one of the pre-eminent Cajun groups.

A few of these songs are archetypes that have burned their way into the American collective musical consciousness: John Estes' "Milk Cow Blues," the Carter Family's "No Depression in Heaven," Joe Williams' "Baby Please Don't Go," and the Monroe Brothers' "Nine Pound Hammer Is Too Heavy."

Other less famous performances are quite intriguing... At 28 songs spread over two CDs, it's a little shorter than might be expected for a box set, though as compensation, it's enclosed in a pretty incredible 96-page liner-note-sized hardcover book with writing by Dick Spottswood and John Fahey.