one of the leading French scholars of the late 19th century, who is best known for his bibliographic and historical studies of medieval France.

Langlois received his doctorate in 1887 and was named lecturer at the faculty of letters of Douai. In 1909 he became a professor at the University of Paris, where he taught paleography, bibliography, and the history of the Middle Ages.

Langlois's work Le Règne de Philippe III le Hardi (1887; “The Reign of Philip III the Bold”), emphasizing the political and institutional conditions of 13th-century France, remains one of the best histories of a single reign. In 1904 he published Manuel de bibliographie historique, 2 vol. (1896–1904; “Manual of Historical Bibliography”), a fundamental work in historical scholarship that provides valuable discussions of bibliographic method.

Among his other treatises are La Vie en France au moyen âge, de la fin du XII^e au milieu du XIV^e siècle, 3 vol. (1925–27; “Life in France in the Middle Ages from the End of the 12th to the Middle of the 14th Century”), a description of French life illustrated by edited selections from medieval texts, and Les Archives de l'histoire de France (1891–93), a bibliographic description of archives in all parts of France. Langlois became director of the Archives Nationales in 1913 and was later appointed to the Académie des Inscriptions et Belles-Lettres (1917).