The music and lyrics of Stephen Sondheim (1930-) have shaped and influenced American musical theater from the mid-twentieth century onward. Sondheim’s vaunted career has been nothing if not diverse in scope and content; however, Sondheim has become particularly known for creating heady, intellectual, and often subversive musicals, incorporating complex music, tightly crafted lyrics, and conceptual innovations. This penchant for innovation has earned Sondheim a reputation as something of an auteur, an artist with a singular vision and approach, which often overshadows the contributions of his collaborators. However, musical theater, by its nature, is a collaborative art form, and as such, to minimize the authorial input of Sondheim’s collaborators is unnecessarily reductive and, ultimately, inattentive to the medium itself. In this thesis, I explore issues of collaboration and reception history through the theoretical lens of authorship, using the musical Assassins, with music and lyrics by Sondheim and a libretto by John Weidman, as a case study. My analysis focuses on the 1990 off-Broadway production and the more successful 2004 Broadway revival, giving an account of the musical’s evolution over time, examining the artistic contributions of Sondheim and Weidman’s collaborators, and teasing out the possible reasons behind the disparate reception histories of both productions. Also of concern is the notion of Sondheim’s “authorial” voice, musically speaking, and how, building upon the work of musicologist Steve Swayne, Sondheim’s frequent use of intertextuality and stylistic imitation puts pressure on the notion of a singular musical voice.