In this paper we propose to address the origins and historical development of the activism of Abuelas de Plaza de Mayo (Grandmothers of the Plaza de Mayo), an Argentine human rights organization that advocates for the location, identification and restitution to their biological families of children appropriated by the Armed and Security Forces during the last dictatorship in that country. We will look at the historical conformation of the organization, first as a group within Madres de Plaza de Mayo and then as an independent association. We will analyze the tactics and repertoire of action that its members deployed during the military regime to search for their grandsons and granddaughters and to denounce their disappearance, both nationally and internationally. Finally, we will address how the organization’s repertoire of action and discourse changed from the post-dictatorship period until the 2000s.