"Rarities"--which collects previously unreleased material, as well as contributions to soundtracks, tribute albums and benefit albums--contains recordings from throughout the duo's nearly two-decade career.

Among the previously unreleased tracks are "Let Me Go Easy," "Winthrop," "Point Hope," a demo of "Ghost" and a remix of "Free In You," according to a press release.

The set also features "Cold as Ice," which was one of Ray's first compositions. "I always felt bad for using a Foreigner title for my song," she said in a statement.

"Walk Your Valley," a Saliers composition that appears on "Rarities," was recorded only once at a soundcheck. "I felt sure no one would have a bootleg copy of this," Saliers said in a press release.

Among the cover songs on the album are The Clash's "Clampdown," Vic Chesnut's "Free of Hope" and The Grateful Dead's "Uncle John's Band."

The latest album of new Indigo Girls material was last year's "All That We Let In," which features Ray and Saliers backed by their longtime band: bassist Clare Kenny, keyboardist Carol Isaacs and drummer Brady Blade. Also featured on the set is singer/pianist Joan Osborne, who contributes back-up vocals to three tracks.