Over the last quarter-century, scholars have taken a unified approach in discussing form in Italian and French opera of the nineteenth century. This approach centers around the four-part aria and duet form begun by Bellini, codified by Rossini, modified by Verdi, and dissolved by Puccini. A similar trajectory can be seen in French opera in the works of Meyerbeer, Gounod, and Massenet; however, only Meyerbeer and Gounod have received significant critical attention. This is in part due to Massenet's reception as a "composer for the people," a title ill fitting and ripe for reconsideration. This dissertation will examine duet forms in Massenet's oeuvre and will focus on the gradual change in style manifest in his twenty-five operas. Massenet's output can be divided into three distinct periods delineated by his approach to form. Representative works from each period will show how he inherited, interpreted, thwarted, and ultimately rewrote the standard formal conventions of his time and in doing so, created a dramaturgical approach to opera that unified the formerly separate number-based elements. Massenet's longevity and popular appeal make him the quintessential French opera composer of the fin de siècle and the natural choice for examining reconstructed conventions.