Rock and roll (often written as rock & roll or rock 'n' roll) is a genre of popular music that originated and evolved in the United States during the late 1940s and early 1950s, primarily from a combination of African American blues, country, jazz, and gospel music. Though elements of rock and roll can be heard in country records of the 1930s, and in blues records from the 1920s, rock and roll did not acquire its name until the 1950s.

The term "rock and roll" now has at least two different meanings, both in common usage. The American Heritage Dictionary and the Merriam-Webster Dictionary both define rock and roll as synonymous with rock music. Encyclopædia Britannica, on the other hand, regards it as the music that originated in the mid-1950s and later developed "into the more encompassing international style known as rock music". For the purpose of differentiation, this article uses the second definition.

In the earliest rock and roll styles of the late 1940s and early 1950s, either the piano or saxophone was often the lead instrument, but these were generally replaced or supplemented by guitar in the middle to late 1950s. The beat is essentially a blues rhythm with an accentuated backbeat, the latter almost always provided by a snare drum. Classic rock and roll is usually played with one or two electric guitars (one lead, one rhythm), a string bass or (after the mid-1950s) an electric bass guitar, and a drum kit.