The first generation of professional ethnologists emerged in the inter-war period in France, with the founding of the Institut d'ethnologie in 1925 and the Musée de l'Homme in 1937. Ethnology, conceived by Paul Rivet as a new humanism, found immediate favour with the public, and the exhibitions at the Musée d'ethnographie du Trocadéro / Musée de l'Homme were crowd-pullers. Large collections also entered the museum at the time, often related to the cultural and human treasures of the French colonies. They were assembled during assignments abroad by the museum's staff and the ethnologists trained at the Institut d'ethnologie, but many other figures were also important: colonial administrators, travelers, explorers and scientists from other disciplines, all of whom tried their hand at ethnological collecting. This Research Paper is based on an analytical study of the private archives, held by the musée du quai Branly, of one such collector, the geologist Edgar Aubert de la Rüe. His assignments in the New Hebrides (today, Vanuatu), French Somaliland (Djibouti) and French Guiana can shed light, from the borders of the field of ethnography, on the history of this constantly evolving discipline in the inter-war period.