One Nation Underground is the debut album by American psychedelic folk group Pearls Before Swine.

It was recorded at Impact Sound in New York City, between May 6–9, 1967, by the Florida-based group, which at that point comprised main songwriter and singer Tom Rapp, Wayne Harley, Lane Lederer, and Roger Crissinger.

The album presents a mixture of styles - "psychedelic folk reminiscent of Donovan collides with Farfisa-driven punk and hard-to-categorize repetitive minimalism, all thrown together with the undisciplined, creative exuberance of youth".

Early vinyl copies came with a small poster of the Hell panel from Hieronymus Bosch's The Garden of Earthly Delights, a detail of which was used on the front of the album sleeve.

On October 20, 2017, Drag City - with the cooperation and participation of Tom Rapp and original engineer/producer Richard Alderson - released a "Fiftieth Anniversary Mono Restoration & Remastering" on CD and LP.