American folk music is a musical term that encompasses numerous genres, many of which are known as traditional music or roots music. Roots music is a broad category of music including bluegrass, country music, gospel, old time music, jug bands, Appalachian folk, blues, Cajun and Native American music. The music is considered American either because it is native to the United States or because it developed there, out of foreign origins, to such a degree that it struck musicologists as something distinctly new. It is considered "roots music" because it served as the basis of music later developed in the United States, including rock and roll, rhythm and blues, and jazz.

Many roots musicians do not consider themselves to be folk musicians; the main difference between the American folk music revival and American "roots music" is that roots music seems to cover a slightly broader range, including blues and country .

Roots music developed its most expressive and varied forms in the first three decades of the 20th century. The Great Depression and the Dust Bowl were extremely important in disseminating these musical styles to the rest of the country, as Delta blues masters, itinerant honky tonk singers, and Latino and Cajun musicians spread to cities like Chicago, Los Angeles, and New York. The growth of the recording industry in the same period was also important; higher potential profits from music placed pressure on artists, songwriters, and label executives to replicate previous hit songs. This meant that musical fads, such as Hawaiian slack-key guitar, never died out completely, since a broad range of rhythms, instruments, and vocal stylings were incorporated into disparate popular genres.

Folk music includes both traditional music and the genre that evolved from it during the 20th century folk revival. The term originated in the 19th century but is often applied to music that is older than that. Certain types of folk music are also called world music.

Traditional folk music has been defined in several ways: as music transmitted by mouth, as music of the lower classes, and as music with unknown composers. It has been contrasted with commercial and classical styles. One meaning often given is that of old songs, with no known composers; another is music that has been transmitted and evolved by a process of oral transmission or performed by custom over a long period of time.

Starting in the mid-20th century a new form of popular folk music evolved from traditional folk music. This process and period is called the (second) folk revival and reached a zenith in the 1960s. This form of music is sometimes called contemporary folk music or folk revival music to distinguish it from earlier folk forms. This type of folk music also includes fusion genres such as folk rock, folk metal, electric folk, and others. While contemporary folk music is a genre generally distinct from traditional folk music, in English it shares the same name, and it often shares the same performers and venues as traditional folk music. Even individual songs may be a blend of the two.

Peter "Pete" Seeger (born May 3, 1919) is an American folk singer and an iconic figure in the mid-20th-century American folk music revival. A fixture on nationwide radio in the 1940s, he also had a string of hit records during the early 1950s as a member of The Weavers, most notably their recording of Lead Belly's "Goodnight, Irene", which topped the charts for 13 weeks in 1950. Members of The Weavers were blacklisted during the McCarthy Era. In the 1960s, he re-emerged on the public scene as a prominent singer of protest music in support of international disarmament, civil rights, and environmental causes.

As a song writer, he is best known as the author or co-author of "Where Have All the Flowers Gone?", "If I Had a Hammer (The Hammer Song)", (composed with Lee Hays of The Weavers), and "Turn, Turn, Turn!", which have been recorded by many artists both in and outside the folk revival movement and are still sung throughout the world. "Flowers" was a hit recording for The Kingston Trio (1962); Marlene Dietrich, who recorded it in English, German and French (1962); and Johnny Rivers (1965). "If I Had a Hammer" was a hit for Peter, Paul & Mary (1962) and Trini Lopez (1963), while The Byrds popularized "Turn, Turn, Turn!" in the mid-1960s, as did Judy Collins in 1964, and The Seekers in 1966. Seeger was one of the folksingers most responsible for popularizing the spiritual "We Shall Overcome" (also recorded by Joan Baez and many other singer-activists) that became the acknowledged anthem of the 1960s American Civil Rights Movement, soon after folk singer and activist Guy Carawan introduced it at the founding meeting of the Student Nonviolent Coordinating Committee (SNCC) in 1960. In the PBS "American Masters" episode Pete Seeger: The Power of Song, Seeger states it was he who changed the lyric from the traditional "We will overcome" to the more singable "We shall overcome".