Present-day Uruguay has been inhabited for about 12,000 years. The Spanish and the Portuguese arrived fi ve centuries ago, marking the beginning of relentless interactions with the several ethnic groups that inhabited the region. The events of the last fi ve centuries have been partially recorded through colonial documents. However, accessing the history that preceded colonization requires archeological work, given that the original peoples were preliterate.Although in some places contact between Spanish and the languages spoken in America continues, in Uruguay, no indigenous language has survived. The absence of native language manifestations leaves us with no option but to resort to written testimonies and offi cial records of the time. But anyone who intends to study Uruguay's autochthonous languages will soon realize with dismay that there are just a few sources available. Unfortunately, these sources do not constitute grammars or thorough vocabularies, making it impossible to reconstruct the languages. 1 National historiography has reasserted the idea that Uruguay is a European country imbedded in America, where the nation's history begins with the arrival of the fi rst Europeans in the 16th century. This narrative presents the Indians as marginal characters in the process of national identity and ignores the fact that some of them, mainly the Guarani Indians of missionary origin and their ancestors, comprised the creole population of Uruguay ( Pi Hugarte 1993 ). Guarani was the language that left the most indelible footprint on the Spanish spoken in Uruguay, a claim supported by the fact that between 1770 and 1780, about half of the population of Uruguay consisted of Guarani Indians who had been born in the Jesuit missions.This chapter discusses the impact of indigenous languages on Uruguayan Spanish. Section 1 presents the original peoples of present-day Uruguay, what we know about the tongues they spoke, and the possible reasons for the extinction of their languages. Section 2 describes the impact of Guarani on Uruguayan Spanish, and Section 3 displays a snapshot of sociolinguistic studies on the vitality of some Guarani loanwords.