Guillaume Grandidier (1873 – 1957) was a French geographer , ethnologist , zoologist who studied the island of Madagascar.
He was the son of the wealthy industrialist Alfred Grandidier also a zoologist and expert on Madagascar. Guillaume Grandidier was Secretary of the Geographical Society of Paris and a prolific author.
He wrote Atlas des Colonies Françaises, Protectorats et Territoires sous Mandat de la France. Société D´Éditions Geographiques, Maritimes et Coloniales. Paris. (1934) , with Petit, G. Zoologie de Madagascar. Société d'Editions Géographiques, Maritimes et Coloniales, Paris 2 ((1932) and edited with his father Collection des Ouvrages Anciens Concernant Madagascar 9 vols. Paris: Comité de Madagascar (1903–1920) and many other works on Madagascar. The best known is the monumental Madagascar L'Histoire politique, physique et naturelle de Madagascar. This work was undertaken in cooperation with his father and others such as Alphonse Milne-Edwards and Leon Vaillant. This work ran to 40 volumes