Blues rock is a subgenre of rock which developed in the late-1960s and which emphasizes the traditional, three-chord blues song and instrumental improvisation.
The first original blues rock artists such as Cream, the Paul Butterfield Blues Band and Canned Heat actually borrowed the idea of combining an instrumental combo with loud amplification from rock and roll, and also attempted to play long, involved improvisations which were commonplace on jazz records and live blues shows.
As blues rock gained popularity, bands that followed immediately were louder and more riff-oriented, giving birth to both heavy metal and Southern rock, which both used basic blues riffs and featured extended solos.
In the early 1970s, the lines between blues rock and hard rock were barely visible, as bands including ZZ Top began recording rock-oriented albums that tended to obscure their blues roots.
However, blues rock soon distinguished itself from hard rock and acts continued to play or rewrite blues standards, as well as write their own songs in the same idiom.