The first comprehensive study of the cathedral's medieval stained-glass windows, supported by restoration charts, was carried out in 1959 by the art historian Jean Lafond and was the first of the collection of French works in the Corpus Vitrearum. Since that date, the publication of the inventory of ancient stained-glass windows in France, as well as other publications, have widened our knowledge of the stainedglass windows of Notre-Dame. The three medieval roses are the most important elements of Notre-Dame's glass heritage. Dating back to the 13 th century, they show evidence of the restorations carried out across the centuries. In the west rose which depicts a psychomachia, the zodiac and the Labours of the Months, only eleven of the original panels are still in place. In the north transept, the rose depicting the Virgin Mary surrounded by figures of the Old Testament is the best preserved window. The rose located in the south, which originally depicted a majestic God presiding over an assembly of saints, virgins and angels, has been substantially modified. A large number of stopgaps are observed in these three roses and are a sign of the restoration techniques used during the 18 th century. The coats of arms of Cardinal and Marshal Noailles, found in one of the choir chapels, are the two last vestiges of this period. The 18 th -century decoration was, in turn, replaced during the restoration of the cathedral by Lassus and Viollet-le-Duc. In keeping with medieval traditions, they sought to present stained-glass windows with large figures in the upper windows of the choir, narrative stained-glass windows in some chapels and grisaille stained-glass windows for the rest of the building. This project took more than ten years to accomplish and was carried out by seven glass painting workshops, chosen amongst the best of their time and assisted by a painter. To restore the missing stained-glass windows, the architects relied on the small number of written reports describing the stained-glass windows before their destruction, but also on the details of fragments remaining in the cathedral, and the stained-glass windows of other medieval buildings. In the second half of the 20 th century, the grisaille windows that had been installed in the nave in the previous century were in turn replaced with abstract windows created by Jacques Le Chevallier. Since 2019, art historians from the Glass working group have been actively committed to updating and synthesizing the historical data on all of the cathedral's stained-glass windows. Documentary research will help to guide the observation of the works and will be completed, in the case of the original stained-glass windows, with the revision of the 1959 restoration chart. The study of the 19 th -century stained-glass windows will focus on the search for archaeological models, on the quality of the materials (glass, lead, etc.) and their implementation, but also on the specificity of the painting work, and ultimately providing a better knowledge of the workshops of glass painters who worked for Notre-Dame.