This study presents research relevant to the performance of four different mezzo-soprano songs from musicals composed by Stephen Sondheim. The research first gives a comprehensive overview of the contributions of Sondheim to the American Musical Theatre genre, and compares and contrasts his treatment of mezzo-soprano characters with that of his contemporaries. The project also investigates details regarding cultural and historical influences over the four musicals. Additionally, the study includes character analyses and musical analyses for each of the selected characters and their respective songs. The research is synthesized in order to provide suggestions of ways mezzo-sopranos can incorporate this research into their performance, in order to give a more informed and educated presentation of the selected pieces. / The contributions of Stephen Sondheim -- Mezzo-sopranos of the American musical -- Amy in Company (1970) -- Beth in Merrily we roll along (1981) -- The bakers wife in Into the woods (1987) -- Lynette "Squeaky" Fromme in Assassins (1990). / School of Music