Mono Masters is a compilation album by the Beatles, and is an alternate, all-mono version of the album Past Masters. Mono Masters was originally a two-CD set included as part of The Beatles in Mono box set. The premise of this box set was to compile only Beatles material which was released or prepared for release with a dedicated mono mix. As a result, the track listing for Mono Masters differs from Past Masters on the second half of disc two, replacing some later songs that never had a mono mix with several songs released on stereo-only albums that had unreleased mono mixes. Tracks 9–12 and 15 of disc two were prepared in March 1969 for release as a 7" mono Yellow Submarine EP, two months after the release of the similarly titled soundtrack album, but the project was scrapped, although the EP was mastered. Instead, the tracks were only released in stereo, while the true mono mixes remained unreleased. "Get Back" was the final Beatles single mixed for mono format. It was released in the UK in mono, though the US release was in stereo. Thus, the songs that were originally released on stereo singles worldwide are omitted on this release.