This article describes the construction of a corpus of spoken French with a time depth of a century and a half, the Récits du français québécois d'autrefois (RFQ). The folktales, local legends, and interviews constituting the RFQ were produced by speakers born between 1846 and 1895. They spoke the French of 19th-century rural Québec, a variety shown to be replete with the vernacular structures and inherent variability of contemporary dialects. The authors review the advantages and drawbacks associated with this type of diachronic material, and argue that, exploited judiciously, it effectively represents an earlier stage of spoken French. They show how systematic comparison of the RFQ with contemporary vernaculars can help pinpoint the existence, date, and direction of language change.The research on which this article is based was generously funded by the Social Science and Humanities Research Council of Canada and a Killam Research Fellowship to Poplack. We are very grateful to friends and colleagues Diane Vincent and Claude Poirier of Université Laval, and especially to archivist M. Jean Coulombe and the staff at the Archives of Folklore there. Without their precious collaboration, this project could not have come to fruition. Carmen LeBlanc and Lauren Willis collected much of the data for the RFQ, and, along with Lyne Klapka and Dawn Harvie, also participated in corpus transcription and correction. Our thanks to them and the other members of the research team at the Sociolinguistics Laboratory, University of Ottawa, for their painstaking work.