"Space Oddity" is a song by the English singer-songwriter David Bowie. It was first released on 11 July 1969 by Philips and Mercury Records as a 7-inch single, then as the opening track of his second studio album, David Bowie. Produced by Gus Dudgeon and recorded at Trident Studios in London, it is a tale about a fictional astronaut named Major Tom; its title and subject matter were partly inspired by the film 2001: A Space Odyssey (1968) and Bowie's feelings of alienation at that point in his career. Its sound departed from the music hall of his debut album to psychedelic folk inspired by the Bee Gees; it was one of the most musically complex compositions he had written up to that point.

The song was rush-released as a single to capitalise on the Apollo 11 Moon landing. It received critical praise and was used by the BBC as background music during its coverage of the event. It initially sold poorly but soon reached number five in the UK, becoming Bowie's first and only chart hit for another three years. Reissues by RCA Records became Bowie's first US hit in 1972, and his first UK number-one in 1975. He re-recorded an acoustic version in 1979. Several promotional videos were produced for the song, including a 1972 one filmed by Mick Rock. It was a mainstay during Bowie's concerts until 1990, after which it was played sporadically until 2002. Bowie revisited the Major Tom character in later singles, notably the sequel song "Ashes to Ashes" (1980).

A range of artists have covered "Space Oddity" and others have released songs that reference Major Tom. A 2013 cover by the astronaut Chris Hadfield gained widespread attention; its music video was the first filmed in space. The song has appeared in numerous films and television series, including The Secret Life of Walter Mitty (2013). In 2019, Tony Visconti remixed Bowie's original recording to mark its 50th anniversary, with a new music video directed by Tim Pope. In later decades, "Space Oddity" is considered one of Bowie's finest recordings and remains one of his most popular songs. It has appeared in numerous "best-of" lists, including the Rock and Roll Hall of Fame's 500 Songs that Shaped Rock and Roll.

Following a string of unsuccessful singles, David Bowie released his music hall-influenced self-titled debut studio album through Deram Records in 1967. The album was a commercial failure and did little to gain Bowie notice, leading to his departure from Deram in May 1968 and becoming his last release for two years. After its commercial failure, Bowie's new manager Kenneth Pitt authorised the production of a promotional film in an attempt to introduce Bowie to a larger audience. The film, Love You till Tuesday, went unreleased until 1984; it marked the end of Pitt's mentorship of Bowie.

The publicity image of a spaceman at work is of an automaton rather than a human being ... and my Major Tom is nothing if not a human being. It came from a feeling of sadness about this aspect of the space thing, it has been dehumanized, so I wrote a song-farce about it, to try and relate science and human emotion. I suppose it's an antidote to space fever, really.

By the end of 1968, Bowie had begun to feel alienation from his career. Knowing Love You till Tuesday did not have a guaranteed audience and would not feature any new material, Pitt asked Bowie to write something new to "demonstrate David's remarkable inventiveness". Bowie wrote "Space Oddity", a tale about a fictional astronaut named Major Tom. Its title and subject matter were influenced by Stanley Kubrick's film 2001: A Space Odyssey, which premiered in May 1968. Bowie said, "I went stoned out of my mind to see the movie and it really freaked me out, especially the trip passage". Other events in Bowie's life influenced the writing of "Space Oddity", including seeing the Apollo 8 Earthrise photograph in January 1969 and his break-up with the dancer Hermione Farthingale the following month. He later said, "It was Hermione who got me writing for and on a specific person". The biographer Marc Spitz stated Bowie's feelings of loneliness and heartache following the break-up inspired "Space Oddity".

One of the first people to hear "Space Oddity" was Calvin Mark Lee, the head of A&R at Mercury Records in London. Lee considered the song "otherworldly" and knew it was Bowie's ticket to be signed by the label. The head of Mercury, Lou Reizner, was unimpressed with Bowie's output and was unwilling to sign him. Eager to sign Bowie, Lee, without Reizner's knowledge, financed a demo session for "Space Oddity". Lee later told Spitz: "We had to do it all behind Lou's back. But it was such a good record."

"Space Oddity" tells the story of an astronaut named Major Tom, the first of Bowie's famous characters. Major Tom is informed by Ground Control that a malfunction has occurred in his spacecraft; but the astronaut does not get the message. He remains in space "sitting in a tin can, far above the world", preparing for his lonely death. In 1969, Bowie compared Major Tom's fate to the ending of 2001: A Space Odyssey, saying: "At the end of the song Major Tom is completely emotionless and expresses no view at all about where he's at. He's fragmenting ... at the end of the song his mind is completely blown – he's everything then." The authors David Buckley and Peter Doggett comment on the unusual vocabulary in the lyrics, such as "Ground Control" rather than "Mission Control", "space ship" rather than "rocket", "engines on" rather than "ignition", and the "unmilitary combination" of rank and first name for the character.