This study seeks to explore the role and significance of aria insertion, the practice that allowed singers to introduce music of their own choice into productions of Italian operas. Each chapter investigates the art of aria insertion during the nineteenth century from varying perspectives, beginning with an overview of the changing fortunes of the practice, followed by explorations of individual prima donnas and their relationship with particular insertion arias: Carolina Ungher’s difficulties in finding a “perfect” aria to introduce into Donizetti’s Marino Faliero; Guiditta Pasta’s performance of an aria from Pacini’s Niobe in a variety of operas, and the subsequent fortunes of that particular aria; Maria Malibran’s interpolation of Vaccai’s final scene from Giulietta e Romeo in place of Bellini’s original setting in his I Capuleti e i Montecchi; and Adelina Patti’s “mini-concerts” in the lesson scene of Il Barbiere di Siviglia.