Bluegrass is a style of southern string band music developed by Bill Monroe in the 1930s and 1940s. Bill Monroe's records with the Blue Grass Boys were so popular on the radio that announcers began using the term "bluegrass music." Typical instrumentation is fiddle, banjo, mandolin, guitar, dobro, and bass. Bluegrass comes from mountain, gospel, and blues music, and generally involves a traditional, often melancholy, subject. It is played by an acoustic string band, which may be augmented by traditional instruments, such as the harmonica, mouth harp, accordion, jug, and spoons. Bluegrass is frequently characterized by virtuoso string playing, as with Monroe playing the mandolin, or Earl Scruggs the banjo; and the mandolin, following Monroe's example, is a prominent part of most bands. The tempo of the music is frequently fast, highlighting the skill of the performers. A striking feature of bluegrass is the intensely high and pure tone of lead vocalists, particularly in songs of longing or loss, as heard in the singing of Ralph Stanley, Alison Krauss, and, of course, Monroe himself.

A style of music originally based on field shouts and secular songs of the American Negro, featuring repeated sections of twelve measures each in an A-A-B structure. This is a vocal genre, often performed by singing guitarists, with melodic lines characterized by flatted thirds and sevenths. Despite the name, the mood can be happy or sad, the tempo fast or slow. Sometimes called a subgenre of jazz, blues music has its own identity in artists such as Buddy Guy and Ruth Brown. Typical artists in blues-rock, a related style, are Stevie Ray Vaughan and Eric Clapton.