This dissertation provides a history of Spanish-Comanche relations during the era of Spanish Texas. The study is based on research in archival documents, some newly discovered. Chapter 1 presents an overview of events that brought both people to the land that Spaniards named Texas. The remaining chapters provide a detailed account of Spanish-Comanche interaction from first contact until the end of Spanish rule in 1821. Although it is generally written that Spaniards first met Comanches at San Antonio de Béxar in 1743, a careful examination of Spanish documents indicates that Spaniards heard rumors of Comanches in Texas in the 1740s, but their first meeting did not occur until the early 1750s. From that first encounter until the close of the Spanish era, Spanish authorities instituted a number of different policies in their efforts to coexist peacefully with the Comanche nation. The author explores each of those policies, how the Comanches reacted to those policies, and the impact of that diplomacy on both cultures. Spaniards and Comanches negotiated a peace treaty in 1785, and that treaty remained in effect, with varying degrees of success, for the duration of Spanish rule. Leaders on both sides were committed to maintaining that peace, although Spaniards were hampered by meager resources and Comanches by the decentralized organization of their society. The dissertation includes a detailed account of the Spanish expedition to the Red River in 1759, led by Colonel Diego Ortiz Parrilla. That account, based on the recently discovered diary of Juan Angel de Oyarzún, provides new information on the campaign as well as a reevaluation of its outcome. The primary intention of this study is to provide a balanced account of Spanish-Comanche relations, relying on the historical record as well as anthropological evidence to uncover, wherever possible, the Comanche side of the story. The research reveals much about the political organization of the Comanche people.