Louis Étienne Joseph Marie de La Vallée-Poussin (1 January 1869 – 18 February 1938) was a Belgian Indologist and scholar of Buddhist Studies.
La Vallée-Poussin was born in Liège, where he received his early education. He studied at the University of Liège from 1884 to 1888, receiving his doctorate at the age of nineteen. He studied Sanskrit, Pali, and Avestan under Charles de Harlez and Philippe Colinet from 1888 to 1890 at the University of Louvain, receiving a docteur en langues orientales in July 1891. Moving to Paris, he began his studies at the Sorbonne that same year under Victor Henri and Sylvain Lévi. During this time (1891–1892), he also occupied the chair of Sanskrit at the University of Liège. He continued his study of Avestan and the Zoroastrian Gathas under Hendrik Kern at Leiden University, where he also took up the study of Chinese and Tibetan. In 1893, he attained a professorship at the University of Ghent teaching comparative grammar of Greek and Latin, a position which he held until his retirement in 1929.