Licensing agencies are companies that handle the purchase of licenses to copyrighted works without having to contact the copyright owner directly.
Much of the licensing of performance rights for musical works published in the United states happens through the following three agencies: ASCAP, BMI, and SESAC (links below). Performance licenses cover uses related to the public performance of copyrighted music, such as concert performances or playing a musical recording in a public space.
Harry Fox Agency offers mechanical licenses for the reproduction and distribution of musical works. This includes digital licenses for uses such as streaming or digital downloads.