Klaatu (/ˈklɑːtuː/) was a Canadian rock group formed in 1973 by the duo of John Woloschuk and Dee Long. They named themselves after an ambassador, Klaatu, from an extraterrestrial confederation who visits Earth with his companion robot Gort in the film The Day the Earth Stood Still. After recording two non-charting singles, the band added drummer Terry Draper to the line-up; this trio constituted Klaatu throughout the rest of the band's recording career.

In Canada, the band is remembered for several hits, including "California Jam" (1974), "Calling Occupants of Interplanetary Craft" (1976), and "Knee Deep in Love" (1980). In the U.S., "Calling Occupants" backed with "Sub-Rosa Subway", was a minor double-sided hit and their only chart entry, peaking at No. 62 in 1977.

Internationally, the group's pop-influenced style of progressive rock has led to them being known as the "Canadian Beatles".

Klaatu has variously been described by critics and journalists as progressive rock, psychedelic pop, pop rock, and space rock.

The band's combination of pop and progressive/art rock has often been compared to the Beatles, the guitar-rock of Queen, the electronic music of Wendy Carlos, the light pop sound of 10cc, and the orchestrated ballads of the Moody Blues and Electric Light Orchestra. British music magazine Shindig! praised the band's "otherworldly brand of progressive pop".

The band, initially a studio-only duo of Woloschuk and Long, released the singles "Anus of Uranus/Sub-Rosa Subway" and "Dr. Marvello/For You Girl" on GRT Records, in 1973, before being taken under the wing of Daffodil Records and its president Frank Davies. With Terry Draper added to the line-up, the singles "California Jam" and "True Life Hero" followed. These early singles credited Dee Long as a writer of several tunes; the others (including "Sub-Rosa Subway", "Dr. Marvello" and the hit single "California Jam") were credited to "Chip Dale," a collective pseudonym for Woloschuk and frequent co-writer Dino Tome. "California Jam" hit the Canadian Top 40, peaking at No. 36, and Klaatu, though they played no live dates, promoted their music by making a television appearance in Canada on the Keith Hampshire-hosted show Music Machine. By 1975, Davies, along with producer Terry Brown, landed the band a deal with Capitol Records in the United States.

Their first album, 3:47 EST (named Klaatu in the US as Capitol Records' executives found the original title too obscure), was released in September 1976, in North America. The band elected to include no photos, no individual musician credits, and no biographical information in the album package; all songs were simply listed as being written and published by "Klaatu." (Note that this collective writing credit covered songs earlier credited solely to Long or to the team of Woloschuk and Tome – even though Tome was not actually a member of Klaatu.) The album was met with moderately positive reviews, but by Christmas of that year, sales had stalled.

In 1977, an article published in the Providence Journal by journalist Steve Smith speculated that 3:47 EST could actually be a release by a secretly-reunited Beatles recording under a pseudonym, leading to widespread rumours. These rumours were fueled by a number of factors, including the fact that their album was released by Capitol Records (also the Beatles' label in North America), the lack of artist and producer credits or photographs in the album packaging, Klaatu's avoidance of public performances, and the fact that the group's vocal and musical style was reminiscent of the Beatles. In addition, Ringo Starr's 1974 album Goodnight Vienna had featured cover art with Starr appearing in place of the character Klaatu from the movie The Day the Earth Stood Still. The album as a whole had a Beatlesque sound. Subsequent to the Beatles rumour, the songs "Sub-Rosa Subway" and "Calling Occupants of Interplanetary Craft" became minor hits for Klaatu in 1977. "Calling Occupants" was covered by the Carpenters that same year, becoming a Top 40 hit worldwide.