In the middle of the 16th century, and for the first time in History, an Empire questions its rights as a conqueror, as well as the rights of the new conquered subjects. Bartolomé de las Casas and Ginés de Sepúlveda defend two historically antagonistic positions and debate on the natural rights of Native Americans. Almost 500 years later, a small group of experts analyze the context, development and consequences of what is considered as the first debate in the History on Human Rights.