In June 1975, thousands of people converged on Mexico City for the United Nations (UN) conference celebrating International Women’s Year (IWY), the first of four UN women’s conferences that would eventually include those in Copenhagen (1980), Nairobi (1985), and Beijing (1995). Scholars and activists regard IWY as a watershed moment in transnational second wave feminism. Billed as the “greatest consciousness-raising event in history,” the IWY events included both an official conference, which offered an unprecedented opportunity to put women at the center of international policymaking, and a parallel nongovernmental organization (NGO) tribune, which launched a new generation of civil society organizations focused on issues related to women and gender. This book’s first part explores the history of the IWY conference. It particularly attends to the ways that geopolitical and institutional rivalries, competing ideologies, and material constraints fostered the idea of IWY, shaped the plan to hold an international conference, and resulted in the Mexico City conference serving as the year’s centerpiece. The second part follows the action in the conference and tribune, including conflicts over representation, sexuality, and human rights. The final part considers IWY’s legacies, which included the creation of enduring transnational NGO networks and far-reaching changes within the United Nations. Although the Mexico City conference is widely remembered for its failure to achieve consensus, this book demonstrates that IWY’s greatest achievements emerged from the moments that invited wide-ranging perspectives and even open conflict.