Henri Gregoire ([ɑ̃ʁi ɡʁeɡwaʁ]; Huy, Belgium, 21 March 1881 – 28 September 1964, Brussels, Belgium) was an eminent scholar of the Byzantine Empire, virtually the founder of Byzantine studies in Belgium.
Gregoire spent most of his teaching career at the Universite libre de Bruxelles. In 1938, he taught at the New School for Social Research and during the Second World War, joined the Ecole libre des hautes etudes at the New School.
He was the editor of four journals—Byzantion, Nouvelle Clio, Annuaire de l'Institut de Philologie et d'Histoire Orientales et Slaves, and Flambeau—and published prolifically: by 1953 he had 575 titles in his bibliography.
Gregoire is especially remembered for his work on medieval epic poetry, notably Digenis Akritas.