Yellow Submarine is the tenth official album released by The Beatles. It was the soundtrack to the animated film of the same name.
In contrast to the richness of the movie, the Yellow Submarine album is usually considered the Beatles' weakest effort, being a soundtrack for the film rather than a studio album in its own right, and featuring only six Beatles songs.
By the time the album came out, much of it was not new. "Yellow Submarine" had already appeared on Revolver in August 1966. "All You Need Is Love" had been a hit single in 1967 and had also appeared on the US edition of Magical Mystery Tour later that year. "Only A Northern Song" was written originally for Sgt. Pepper. Most of it was recorded in February 1967. "It's All Too Much" was recorded just before Sgt. Pepper came out, although it was shortened (from eight minutes) for Yellow Submarine. "Hey Bulldog" (recorded February 1968) and "All Together Now" (May 1967) appear to have been written specially, although Lennon was dismissive about the former, which was recorded during filming of a promotional clip for "Lady Madonna". 
The second side features arrangements (recorded specifically for the album) of George Martin's orchestral score.
"Across the Universe" was originally slated for the album, but was scrapped at the last moment and was instead put on hold, appearing on a World Wildlife Fund charity album and later on Let It Be. The Beatles considered releasing Yellow Submarine as a five-track EP, without the film score but including "Across the Universe" as a bonus track. 
With the re-release of the film in 1999, the original album was re-released, along with a "songtrack" album (see below).
In 1999, United Artists and Apple digitally restored the film for theatrical and home video re-release. This included cleaning the original film negative and rejuvenating the colour.
The film's soundtrack also was upgraded. All The Beatles songs were remixed in Dolby Digital 5.1. Also, the sound effects were digitally taken apart and rechanneled to conform to the onscreen action. However, because the original 1968 George Martin soundtrack score existed only in mono, Apple replaced certain sections of the score with the re-recorded stereo versions where appropriate.
The film was also re-edited to its original European theatrical release version, with the "Hey, Bulldog!" number restored (whereas the U.S. version deleted this song and replaced it with alternate animation).
To accompany the re-release of the film, a new version of the album (Yellow Submarine Songtrack) was released in 1999, with only The Beatles tracks used in the film (the extra tracks replaced the Martin score tracks from the original album). The songs were fully remixed from the original multitrack tapes for this release, something not done for the original CD release of The Beatles catalogue in the late 1980s (except for Help! and Rubber Soul). All of the Beatles songs included in the film were on the Songtrack, with the exception of "A Day In The Life", which was not put in because EMI did not want too many songs from the Sgt. Pepper album to be on the Songtrack.