The word "klezmer" (derived from the Hebrew "vessel for music") originally referred to a musician, but in the 20th century came to refer to the musical style instead. The origins of klezmer lay in various Jewish folk music traditions from eastern Europe, which drew heavily on local folk traditions, near eastern music, and the cantorial-style chanting of the Jewish synagogue. In the late 19th and early 20th centuries these traditions were influenced in Europe by gypsy and military band styles, and when brought to the United States by Jewish immigrants in the 20th century were further influenced by jazz and stage music.
The music originally consisted of instrumental accompaniment to the various dances and ceremonies associated with celebrations (particularly weddings and bar mitzvahs). With the assimilation of Jews in the U.S., klezmer experienced a severe decline in popularity, but a resurgence in the 1970's resulted in numerous groups taking up the style in the latter portion of the 20th century.
In addition to eastern European-derived pieces, the modern klezmer repertoire is typically augmented by Israeli folk music, tunes from early 20th-century American Yiddish theatre productions, and modern compositions in the traditional style. There are also klezmer fusion groups which integrate rock, bluegrass, reggae and hip-hop into the genre.