Christoph Willibald Gluck’s opera Armide (1777) is an anomaly within the context of his eighteenth-century operatic reform. While all of Gluck’s other libretti had been written as an embodiment of the operatic reform, including his Italian works Orfeo ed Euridice (1762) and Alceste (1767) in addition to the French operas Iphigénie en Aulide (1774) and Iphigénie en Tauride (1779), Armide was based upon the seventeenth-century libretto that Phillipe Quinault had written for Jean-Baptiste Lully, the founder of French tragédie lyrique. The use of Quinault’s libretto drew a direct comparison not only between Gluck and Lully, but also between Gluck and traditional French opera. Setting Armide also required Gluck to incorporate many traditional elements of tragédie lyrique absent in the operatic reform, such as divertissement and ballet. Armide’s departure from the tenets of the reform were so significant that they were criticized by Gluck’s French librettist François-Louis Gand LeBland Du Roullet, who found particular fault with the opera’s lack of dramatic veracity. It is the very incongruity of Armide—its utilization of an antiquated libretto—that makes it key to understanding Gluck’s conception of eighteenth-century opera. Armide provides the best opportunity to explore how Gluck amalgamated the traditional forms and styles of French opera with the goals of Viennese operatic reform. Drawing out connections between tragédie lyrique and the precepts of his reform, Gluck demonstrated the composer’s role in strengthening and clarifying the reform qualities as expressed by the libretto. Through musical analysis, this thesis demonstrates that Armide maintains the musical characteristics and dramatic musical construction of Gluck’s earlier reform operas. It also illustrates that while Gluck honoured Lully’s conception of tragédie lyrique, he did not hesitate to improve what he saw as the faults of the earlier operatic style. Gluck’s juxtaposition of the Italian and French operatic traditions in Armide elucidates his creation of supranational opera. Superseding and encompassing both the French and Italian national styles, Gluck enlivened the operatic traditions of both countries while remaining true to his own dramatic and musical conception of opera.