This project investigates the distribution and use of the possessive form vuestro/a‘your-PL’ in Cusco Spanish. This phenomenon, which has gone mostly unnoticed by scholars so far, is very unusual in Latin American Spanish. The purpose of our investigation is to document its distribution and analyze its origins and productive use in the region. Our hypotheses cover different historical aspects, language contact and local identity as a possible multiclausal explanation. To check these hypotheses, we draw on historical data on colonial and early post-independence Spanish, as well as on corpus data of current Cuzco Spanish, sociolinguistic interviews and elicitation experiments.