|Stylistic Origins:||Blues (esp. electric)|
Rock and roll
|Cultural Origins:||early 1960s in England and United States|
|Instruments:||Electric guitar, Bass guitar, drums, vocals, Hammond organ, Harmonica|
|Popularity:||Peak popularity in the 1960s and 1970s.|
|Derivatives:||Heavy metal  - Hard rock - Boogie rock|
Blues-rock is a hybrid musical genre combining bluesy improvisations over the 12-bar blues and extended boogie jams with rock and roll styles. The core of the blues rock sound is created by the electric guitar, bass guitar and drum kit, with the electric guitar usually amplified through a tube guitar amplifier, giving it an overdriven character.
The style began to develop in the mid-1960s in England and the United States, as what one music critic called a "genre of rhythm'n'blues played by white European musicians". UK Bands such as Led Zeppelin, The Animals, Cream and The Rolling Stones experimented with music from the older American bluesmen like Howlin' Wolf, Robert Johnson, Jimmy Reed and Muddy Waters. While the early blues-rock bands "attempted to play long, involved improvisations which were commonplace on jazz records", by the 1970s, blues rock got heavier and more riff-based. By the "early '70s, the lines between blues-rock and hard rock were barely visible", as bands began recording rock-style albums. In the 1980s and 1990s, blues-rock bands returned to their bluesy roots, and some of these bands, such as the "Fabulous Thunderbirds and Stevie Ray Vaughan flirted with rock stardom." 
Blues-rock can be characterized by bluesy improvisation, the 12-bar blues, extended boogie jams typically focused on the electric guitar player, and often a heavier, riff-oriented sound and feel to the songs than might be found in traditional Chicago-style blues. Blues rock bands "borrow[ed] the idea of an instrumental combo and loud amplification from rock & roll". It is also often played at a fast tempo, again distinguishing it from the blues.
The core of the blues rock sound is created by the electric guitar, bass guitar and drum kit. The electric guitar is usually amplified through a tube guitar amplifier or using an overdrive effect. Often two guitars are played in blues rock bands, one playing the accompaniment riffs and chords on rhythm guitar and one playing the melodic lines and solos of the lead guitar part. While 1950s-era blues bands would sometimes still use the upright bass, the blues rock bands of the 1960s used the electric bass, which was easier to amplify to loud volumes. Keyboard instruments such as the piano and Hammond organ are also occasionally used. As with the electric guitar, the sound of the Hammond organ is typically amplified with a tube amplifier, which gives a growling, "overdriven" sound quality to the instrument. Vocals also typically play a key role, although the vocals may be equal in importance or even subordinate to the lead guitar playing as well, a number of blues-rock pieces are instrumental-only.
Blues-rock pieces normally follow the 12-bar blues structure, but often follow a slightly different structure, as seen in the Allman Brothers version of the T-Bone Walker song "Stormy Monday", which follows the general format of a 12-bar blues, but with altered chords, playing:
G9 | C9 | G9 | G9 | C9 | C9 | G9 / A minor7 | B minor7 / B♭7 | A minor7 | A♭ major7 | G9 / C9 | G9 / D augmented...instead of the expected G | C | G | G | C | C | G | G | D | C | G | G (D) progression. The progression is usually repeated, with only one section of the song, though there are exceptions, some pieces having a "B" section. The key is traditionally major, but can also be minor, a common technique being the use the minor pentatonic scale, with blue notes, over a major chord progression, as employed by Albert King in nearly all of his pieces. The lead guitar typically uses the pentatonic scale, either major or minor, when soloing.
A classic example of blues-rock is Cream's "Crossroads" on "Wheels of Fire" album, adapted from Robert Johnson's "Cross Road Blues" and "Traveling Riverside Blues". It fuses some of the lyrical and musical styles of blues with rock-styled tempo and guitar solos.
While rock and blues have historically always been closely linked, blues-rock as a distinctly recognizable genre did not arise until the late 1960s. In 1963 American guitarist Lonnie Mack developed the guitar style which came to be identified with blues-rock. That year, he released several full-length rock guitar instrumentals strongly grounded in the blues, the best-known of which are the hit singles "Memphis" (Billboard #5) and "Wham!" (Billboard #24). However, blues-rock was not considered a distinct movement within rock until a few years later, with the advent of such British bands as Free, Savoy Brown and the earliest incarnations of Fleetwood Mac, whose members had honed their skills in a handful of British blues bands, primarily those of John Mayall and Alexis Korner. At that point, Mack's recordings were rediscovered and he, too, came to be regarded as a blues-rock artist. Other American performers, such as Johnny Winter, Paul Butterfield and the group Canned Heat are also considered blues-rock pioneers.
Music critic Piero Scaruffi argues that the blues-rock genre was defined when John Mayall released the album Bluesbreakers in 1966, which included guitarist Eric Clapton. Scaruffi defines "blues-rock" as a "genre of rhythm'n'blues played by white European musicians." Scaruffi claims that the US "equivalent of John Mayall was Al Kooper." Cream "took the fusion of blues and rock to places where it had never been before" by engaging in a "level of group improvisation that was worthy of jazz." He calls Fleetwood Mac (during the Peter Green period in the late 1960s) "one of the most creative and competent British bands of the blues revival."  blues. Scaruffi argues that the "British blues musicians were true innovators", in that they did a "metamorphosis" on US blues and "turned it into a "white" music" by emphasizing "the epic refrains of the call and response", speeding up the "Chicago's [([[Chicago Blues]])] rhythm guitars," smoothing "the vocal delivery to make it sound more operatic" and adding vocal harmony.
The revolutionary electric guitar playing of Jimi Hendrix (a veteran of many American rhythm & blues and soul groups from the early-mid 1960s) and his power trios, The Jimi Hendrix Experience and Band of Gypsys, has had broad and lasting influence on the development of blues-rock, especially for guitarists. Eric Clapton was another guitarist with a lasting influence on the genre; his work in the 1960s and 1970s with John Mayall and the Bluesbreakers, The Yardbirds, supergroups Blind Faith, Cream and Derek and the Dominos, and an extensive solo career has been seminal in bringing blues-rock into the mainstream.By this time, American acts such as The Doors and Janis Joplin further introduced mainstream audiences to the genre.
In the late '60s Jeff Beck a former member of The Yardbirds, revolutionised blues rock into a form of heavy rock, taking the UK and the USA by storm with his band, The Jeff Beck Group. Jimmy Page, a third alumnus of The Yardbirds, went out to form The New Yardbirds which would soon become known as Led Zeppelin. Led Zeppelin was a huge force in the early 70s blues-rock scene. The Australian band AC/DC were also influenced by blues rock. Other blues-rock musicians influential on the scene in the 1970s included Rory Gallagher and Robin Trower.
Beginning in the early 1970s, American bands such as Aerosmith fused blues and heavy metal similar to the way that Led Zeppelin had just a few years earlier. Blues-rock grew to include Southern rock and hard rock bands like the Allman Brothers Band, ZZ Top and Lynyrd Skynyrd while the British scene — except for the advent of groups such as Status Quo and Foghat became focused on heavy metal innovation. Blues-rock had a re-birth in the early 1990s, with many artists such as Gary Moore, The White Stripes, John Mayer, The Black Crowes, The Black Keys, The Jon Spencer Blues Explosion, Silvertide, Rachael Yamagata and Joe Bonamassa.
For a longer list of blues rock groups and artists, see the List of blues-rock performers.