Heat of the Day investigates the ways race, gender, and nationality intersected in the international sphere during the 1880s - 1920s. It does so by exploring the life, career, and networks of Mary Church Terrell, an African American feminist prominent on the international stage, as a window into the international activism of African American women. More than any other black woman during this time, Terrell frequently crossed the Atlantic - spending a substantial amount of time in Germany and a few other surrounding European countries; however, the story of her international career remains unwritten. As such, Mary Church Terrell is our entry into a very important shift in how black women understood internationalism. Terrell’s involvement in U.S. interracial cooperative organizing, combined with her cosmopolitanism, help to center African American women in national and global politics. The emergence of transatlantic feminist organizing at the end of the nineteenth century offered black women a new avenue through which to advance their own agenda for racial justice and gender equality by cultivating relationships with leading North American and European feminists. The dissertation argues that Mary Church Terrell changed the way people discussed race in transnational feminist organizing circles and in the international sphere more broadly. She forced her white American feminist colleagues to engage in conversations about race. As an African American activist who engaged in trans-Atlantic debates, Terrell taught European feminists about the authority of black women and helped them understand how race impacted their lives; and, therefore that the world worked differently for her. In all, Heat of the Day contributes to the thriving field of black international history.