The Improbable Conquest offers translations of a series of little-known letters from the chaotic Spanish conquest of the Río de la Plata region, uncovering a rich and understudied historical resource. These letters were written by a wide variety of individuals, including clergy, military officers, and the region’s first governor, Pedro de Mendoza. There is also an exceptional contribution from Isabel de Guevara, one of the few women involved in the conquest to have recorded her experiences. Writing about the conditions of settlements and expeditions, these individuals vividly expose the less glamorous side of the conquest, narrating in detail various misfortunes, infighting, corruption, and complaints. Their letters further reveal the colony’s fraught relationship with the native peoples it sought to colonize, giving insight into the complexities of the conquest and the colonization process. Pablo García Loaeza and Victoria Garrett provide an introduction to the history of the region and the conquest’s key players, as well as a timeline and a glossary explaining difficult and archaic Spanish terms.