Avant-prog is a subgenre of Progressive Rock that emerged around the late 1960s and early 1970s. While progressive rock bands infuse Rock with elements from more traditional forms of Western Classical Music and Jazz, avant-prog artists draw more inspiration from Modern Classical and Avant-Garde Jazz, as well as the unorthodox instrumentation and techniques of Experimental Rock. The music is highly complex and densely arranged, sometimes involving a certain degree of improvisation but for the most part carefully composed (although many bands have recorded entirely improvised pieces as well). Avant-prog tends to be more abstract in nature than other styles of progressive rock, and as such many artists make exclusively instrumental music. If there are vocals they're often wordless, or in certain cases sung in a language invented by the artist. This is particularly common for vocal pieces in the Zeuhl subgenre.

Frank Zappa's work with the Mothers of Invention could arguably be considered the earliest example of avant-prog. The genre rose to prominence through Henry Cow and the Rock in Opposition movement, involving bands such as Univers zéro and Samla Mammas Manna. Avant-prog never gained any real mainstream recognition, but the genre has remained active and popular in underground circles.