This article presents an edition and the first ever translation into Spanish of two Latin epistles on the evangelization of the New World by Juan de Zumárraga and Juan Bernal Díaz de Luco. These epistles have survived in a one sole copy, currently kept at the Biblioteca Capitular y Colombina de Sevilla, that was probably printed in 1533. The article also offers a succinct historical context for both letters and sketches a circle of reformist Catholics, of which Zumárraga and Luco partook during the 1530s, who were concerned about the wellbeing and the evangelization of the indigenous peoples of the Americas.