Apollo 18 is the fourth studio album by American alternative rock duo They Might Be Giants, released in 1992. It was released through Elektra Records and was named after the canceled Apollo 18 mission. The album was also associated with International Space Year, for which They Might Be Giants were declared the official "musical ambassadors" by NASA.

The album marked the first conscious effort by John Linnell and John Flansburgh to branch out of their early sound, opting for more traditional rock rhythms and fuller arrangements. The duo adopted a backing band with live drums during the supporting tour, with Apollo 18 being their last album recorded as only a duo.

Apollo 18 also includes the "Fingertips" suite, a series of twenty-one short songs, most under thirty seconds long. The album generated three singles, "The Statue Got Me High", "The Guitar (The Lion Sleeps Tonight)" and "I Palindrome I", although only "The Statue Got Me High" and "The Guitar" charted.

The album received mostly positive reviews from music critics, with many commending the band for making music with a darker tone. However, the album was criticized for lacking a standout lead single. Commercially, the album was not as successful as Flood (1990), peaking at number 99 on the Billboard 200 and spending only six weeks on that chart. In addition, some fans were upset that Flansburgh and Linnell opted to use a backing band for the album's tour.

"Having the freedom to do the production on the entire record has been very positive. The writing and recording were our only focus for nine months. We purposely avoided session-man-mania, and let our own humble playing shine through."

After the major success of Flood (1990), Elektra sought out Elvis Costello to produce Apollo 18; however, John Linnell and John Flansburgh elected to produce the album themselves as they had originally planned. Prior to recording, the band upgraded many of their instruments; Flansburgh purchased a Marshall amp and Linnell bought several new saxophones. The album was recorded at The Magic Shop in New York City in approximately ten weeks. Although the band recorded Apollo 18 primarily as a duo, its production is musically sparser than that of previous releases. The album's associated tour, the Don't Tread on the Cut-Up Snake World Tour 1992, was the band's first to use a live backing band, rather than a tape deck playing backing tracks. Linnell later noted that this led to much more complicated and deliberate rehearsals.

The music found on Apollo 18 is slightly darker in tone and mood than the songs found on Flood. When it came to writing songs for the album, Linnell and Flansburgh used "old standbys", such as producing harmonies through improvisation and generating melodies by sampling sounds in varying cycles. However, according to the album's press release, Flansburgh and Linnell both sought to expand their horizons and incorporate new sounds and "extreme song arrangements".

The album's opening track, "Dig My Grave", has been described by Parry Gettelman of the Orlando Sentinel as "an angry, fuzzed-out rocker". The vocals for the track were recorded through a guitar fuzz box in order to distort them. "I Palindrome I" originated as a demo written by John Flansburgh for the band's "Dial-A-Song" service. John Linnell later adapted the lyric after attending a reading by the American poet Hal Sirowitz.