Celtic Frost () was a Swiss heavy metal band from Zürich. They are remembered for their strong influence on the development of several metal subgenres, particularly extreme metal, and for their avant-garde approach to music in general.

In June 1984, guitarist and vocalist Thomas Gabriel Fischer and bassist Martin Eric Ain formed Celtic Frost after disbanding their previous band, Hellhammer, a month earlier. Celtic Frost's debut record, Morbid Tales, was released in November of that year. This was followed by the full-length studio albums To Mega Therion (1985) and Into the Pandemonium (1987). All three records are considered highly influential landmarks in heavy metal. While each contains elements of avant-garde composition, Into the Pandemonium is particularly noted for its unique style and experimentation with musical boundaries beyond the heavy metal genre.

Celtic Frost's next album, Cold Lake (1988), featured a new lineup and a dramatic stylistic shift, which was widely criticized for its commercial and flamboyant tone. After releasing Vanity/Nemesis (1990), the band temporarily disbanded. Celtic Frost re-formed in 2001 and released the critically acclaimed Monotheist (2006), eventually disbanding permanently following Fischer's departure in 2008.

Throughout the band's career, their music incorporated elements from various extreme metal styles. Their early work is often classified as thrash metal or black metal with experimental tendencies, while their final album is described as doom metal. Celtic Frost drew inspiration from early heavy metal bands such as Black Sabbath, Judas Priest, and Venom, gothic rock acts like Bauhaus, Siouxsie and the Banshees, Christian Death, and Joy Division, as well as hardcore punk groups like Discharge and GBH.