"What's the New Mary Jane" is a song written by John Lennon and performed by The Beatles. It was recorded in 1968 for the album The Beatles (aka "The White Album"), but never used. "What's the New Mary Jane" is similar to "Revolution 9" in many ways.

‘Mary Jane' was recorded on 14 August 1968 during the recording sessions for the Beatles tenth album The Beatles (aka "The White Album"), with Lennon and George Harrison being the only band members playing on the track. Four takes were recorded with the final being marked as the best. It was later mixed in mono on 26 September with Glass Onion, Happiness Is a Warm Gun and I Will and on the 10 October before being added to the short list for the new album. However during the album's final mixing stage, it was dropped due to time constraints, bringing the album to around 30 songs.

After the release of The Beatles Lennon was still adamant to see the song released. So on November 26, 1969, he and wife Yoko Ono recorded further overdubs with plans for it to be issued as a single by The Plastic Ono Band alongside another unreleased song at the time "You Know My Name (Look Up The Number)" (which was issued as the B-side of The Beatles' "Let It Be" single in 1970). But when the other Beatles heard of John's plans to release a Beatle track under his own band's name the single was pulled. After that, the song had finally been planned to be issued on the album Sessions in 1985, but the album was killed due to objections by the Beatles. The song was held off another 10 years, during which time it gained a certain aura of mystery. During this time, it could only be heard via bootlegs like Esher Demos, From Kinfauns to Chaos, Ultra Rare Trax Vol.5, and What A Shame, Mary Jane Had A Pain At The Party, which is an album that is solely dedicated to this song. A newly mixed version of the recording was finally officially released on the 1996 compilation Anthology 3.

During an interview, Lennon commented on "What's The New Mary Jane", saying, "That was me, Yoko, and George sitting on the floor at EMI fooling around. Pretty good, huh?"