A type of rock which experiments with the basic elements of the genre and/or which pushes the boundaries of common composition and performance technique, such as by use of unusual time signatures, instrumental tunings, compositional styles, lyrical techniques, elements of other musical genres, singing styles or instrumental effects.

The mid- to late 1960s was an era of explosive growth and experimentation in rock music. Bands drew influences from free jazz artists such as John Coltrane and Sun Ra and avant-garde composers like John Cage and Stockhausen. Notable experimental bands in this period include the Velvet Underground, Captain Beefheart and the Magic Band, and the Mothers of Invention.

Influenced by the experiments of these groups came another wave of experimental rock bands in the early 1970s. There was, for instance, the so-called krautrock scene in Germany, which included psychedelic and improvisational bands like Amon Düül II, Faust and Can. Brian Eno was another important figure, especially after his departure from Roxy Music in order to pursue his own ideas (which ultimately led to his invention of the term 'ambient music').

Some other artists in this period, such as David Bowie and Scott Walker, were also departing from more pop-oriented styles in order to experiment with songwriting and production.

At the same time, there was the experimental wing of the already somewhat experimental progressive rock scene, including a number of bands who were influenced by contemporary classical music, such as Henry Cow.