The Blues has its roots in African-American folksongs, adding in some European melodies. It is usually played with guitar, banjo, and the harmonica using techniques from other genres, such as the gospel technique of call-and-response, and the trademark 12-bar rhythm. Blues lyrics lean toward soul-searching and bearing grievances, striking a chord in many listeners. An often popular, even stereotypical method is the way a blues song will say one line, repeat it again, then conclude with a different line. A good example is a song by Tracy Chapman called "Give Me One Reason".
Blues started sometime after the Emancipation Proclamation, from songs sung by African-Americans during slavery. Some of the original Blues lyrics were often filled with racy images, leading to it often being shunned by conservative groups. The then-budding record industry of the twenties didn’t see much of a difference between the Blues and another up-and-coming music genre, Country. They also categorized it as 'race music', much the same as R&B.
An influential person at the time was W.C. Handy, often called 'The Father of the Blues. His songs worked their way into many African-American clubs, and eventually into Caucasian circles. At this time, the slide guitar, a technique where guitar is played with a knife or bottleneck, became an influential part of Delta blues. After WWII, there was more of an emphasis on using electric guitars, which definitely had a major influence on the creation of Rock 'n Roll in the fifties. Several of the artists, such as Bo Diddley and and B. B.King, crossed over into rock.
Blues has continued to thrive, as Blues festivals and clubs embrace the tradition. Some artists, such as Stevie Ray Vaughan and Eric Clapton, have combined with rock to create a new sound.