The thirty Guaraní missions of the Río de la Plata were the largest and most prosperous of all the Catholic missions established throughout the frontier regions of the Americas to convert, acculturate, and incorporate indigenous peoples and their lands into the Spanish and Portuguese empires. But between 1768 and 1800, the mission population fell by almost half and the economy became insolvent. This unique socioeconomic history provides a coherent and comprehensive explanation for the missions' operation and decline, providing readers with an understanding of the material changes experienced by the Guaraní in their day-to-day lives.