A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the Sun. Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew.

A fish is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits. Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians. In a break to the long tradition of grouping all fish into a single class (Pisces), modern phylogenetics views fish as a paraphyletic group.

The Rainbow Fish is a children's picture book drawn and written by Swiss author and illustrator, Marcus Pfister, and translated into English by J. Alison James. The book is best known for the distinctive shiny foil scales of the Rainbow Fish. Decode Entertainment turned the story into an animated television series of the same name, which aired on the HBO Family television channel in the United States and Teletoon in Canada from 1999 until 2000. The book has been criticized for "promot[ing] socialism" and "collectivist" values in a children's book, with some saying that "...[the Rainbow Fish] only gets truly ostracized because he won't hand over his body parts on demand, in the name of equality."