Rainbow (also known as Ritchie Blackmore's Rainbow or Blackmore's Rainbow) are a British rock band formed in Hertford in 1975 by guitarist Ritchie Blackmore. Established in the aftermath of Blackmore's first departure from Deep Purple, they originally featured four members of the American rock band Elf, including their singer Ronnie James Dio, but after their self-titled debut album, Blackmore fired these members, except Dio, recruiting drummer Cozy Powell, bassist Jimmy Bain, and keyboardist Tony Carey. This line-up recorded the band's second album Rising (1976), while Long Live Rock 'n' Roll (1978) saw Bob Daisley and David Stone replace Bain and Carey, respectively. Long Live Rock 'n' Roll was also the last album with Dio before he left the band to join Black Sabbath in 1979.

Rainbow's early work primarily used mystical lyrics with a hard rock/heavy metal style, then went in a more pop-rock oriented direction following Dio's departure from the group. In 1979, Blackmore and Powell revamped the group, recruiting three new members—singer Graham Bonnet, keyboardist Don Airey and another then-former Deep Purple member, bassist Roger Glover—and this line-up gave the band their commercial breakthrough with the single "Since You Been Gone" from their fourth studio album Down to Earth. With Joe Lynn Turner, who replaced Bonnet in 1980, Rainbow recorded three more albums—Difficult to Cure (1981), Straight Between the Eyes (1982) and Bent Out of Shape (1983)—that had commercial success similar to the band's previous albums. Other members of the band during this period were drummers Bobby Rondinelli and Chuck Burgi and keyboardist David Rosenthal. The band split in 1984, when Blackmore and Glover re-joined Deep Purple. In 1993, after leaving Deep Purple for a second time, Blackmore reformed Rainbow with a new line-up, fronted by a then-unknown Doogie White, which recorded their eighth and last studio album to date Stranger in Us All (1995). Blackmore's change in direction, from rock to Renaissance and medieval-influenced music, led to Rainbow's second dissolution in 1997. He revived the band once again in 2015, and they performed live occasionally within the next few years.

Over the years Rainbow went through many personnel changes, with each studio album recorded with a different line-up, leaving Blackmore as the band's only constant member. Their longest serving lineup—which featured Blackmore on guitar, Blackmore's wife Candice Night on backing vocals, Ronnie Romero on lead vocals, Bob Nouveau on bass, David Keith on drums and Jens Johansson on keyboards—lasted from 2015 to 2023, when Romero announced his departure from the band.

Rainbow were ranked No. 90 on VH1's 100 Greatest Artists of Hard Rock. The band have sold over 28 million records worldwide.