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 work examines the history, the actions and legacies of the IWY conference.