This thesis examines the role of advocacy and social justice in the music of three living American women composers, and the ways their efforts as mentors, patrons, academics, and educators interact with their work as composers. Case studies include Gabriela Lena Frank (b. 1972), Missy Mazzoli (b. 1980), and Jennifer Jolley (b. 1981). My musicological narrative is informed by Kimberly Francis’s concept of women as “cultural mosaics” and Patricia Hill Collins’s theorization of intersectionality, which addresses the junction of variable characteristics (such as race, gender, or class) as they relate to an individual’s identity. I have centered my narrative on social issues these composers address through their activism and their music. Gabriela Lena Frank’s orchestral work, Peregrinos (2009), emphasizes Frank’s value of community outreach and her interdependence on others. Frank uses folklórica traditions and Latin mythology to musically recognize the diverse experiences of Latin American immigrants living in Indianapolis. Missy Mazzoli blends operatic traditions with electronics to convey messages of female empowerment in Song from the Uproar: The Lives and Deaths of Isabelle Eberhardt (2012). Mazzoli’s characterization of the fascinating life of this nineteenth-century woman resonates with modern understandings of intersectionality and agency, and aligns with her work with the Luna Composition Lab. Jennifer Jolley’s approach to musical activism in Prisoner of Conscience (2017) mirrors her philosophical and political messages explored on her blog and e-magazine articles. Juxtaposing punk rock with church motets and madrigals, Jolley comments on the nature of protest and the punishment of Russian feminist punk group, Pussy Riot. I position these composers as cultural agents with diverse concerns and diverse means by which to voice them. Frank, Mazzoli, and Jolley each participate in valuable extra-musical roles outside of their compositions: from Gabriela Lena Frank’s Creative Academy of Music, to Mazzoli’s Luna Composition Lab, to Jolley’s NewMusicBox articles. Each of these composers negotiate agency within traditions that have not always been open to women, and they seek to further remedy race and gender inequities through their prominent positions as educators and composers.