Lili Boulanger's (1893-1918) World War I compositions, along with her war charity work and her intentional representation of maternal gender roles, both challenge and broaden the conventional masculine narratives of the First World War and French cultural identity. Boulanger and her colleagues, critics, family, and friends mobilized her femininity to support dominant contemporary conceptions of French wartime motherhood, the marraine de guerre (godmother of war), the femme fragile, and the Catholic Good Sufferer. Her music adds a transformative layer to the traditional musical wartime narrative, as it highlights and explores subjects that her male contemporaries did not broach, such as melancholia and motherhood. Through an analysis of Boulanger's reception, her compositions written and/or performed during the First World War, and her constructed public and private personae, I examine how she became, at various times, a marraine de guerre, a Mimi Pinson, or a Thérèse of Lisieux figure. Boulanger was a central performer of noble feminine suffering during the war and an emblematic symbol of an artistic, musical France. I also explore how her compositions exemplified contemporary French musical styles that musicians fervently debated and defined as key to musical French identity. Boulanger's music thus remains vital to the history of both French wartime music and World War I France. Chapter One analyzes Boulanger's representations of wartime motherhood and melancholia in Dans l'immense tristesse. Chapter Two examines the theme of Good Suffering in several of her compositions, including the settings of Psaumes 129 and 130. Chapter Three argues that Boulanger assumed the role of the marraine de guerre by playing an active role as "secretary-founder" of the Comité Franco-Américain and its subsequent Gazette. Chapter Four explores the contents of the Gazette as a tangible document of Boulanger's wartime work, musician-soldiers' lives at the front, and their engagement with debates on musical Frenchness and the war. Chapter Five demonstrates Boulanger's critical participation in defining musical Frenchness through both her consumption and production of musical exoticism, as shown in an analysis of Maïa and Vieille prière bouddhique.