Online harassment increasingly targets teenage girls, and it has life-changing consequences. Through a triangulation of historical analysis, community-engaged research and in-depth interviews, this dissertation explores the impact of online harassment on girls’ identity, privacy and speech. Its historical analysis explores discipline and resistance across institutions and eras, identifying the long-standing dynamics that underpin girls’ experiences of online harassment today. In its findings, this project identifies three contemporary phenomena that shape girls’ experiences online. First, the concept of “platform coverture,” which works to foreclose girls’ agency and shape their identity-development against the threat of online harassment. Second, the idea of “presumptive exposure,” a feeling that girls carry with them across physical and digital spaces because of sexualized online harassment. Third, the “speech/silence” bind, which compels girls to both speak and censor themselves to avoid online harassment. Ultimately, this dissertation argues that the current “crisis” discourse surrounding girlhood and technology obscures more than it reveals. By way of conclusion, it offers new approaches to conceptualizing girlhood and recommendations for stemming the rise of online harassment.