Willem F. H. Adelaar (born 1948 at The Hague) is a Dutch linguist specializing in Native American languages, specially those of the Andes. He is Professor of indigenous American Linguistics and Cultures at Leiden University. In 1994 he was given a newly created Professorial chair in "Languages and Cultures of Native America" at the University of Leiden. He is noted for his belief that the linguistic diversity of the Americas suggests a deeper history of population than the standard account of the settlement of the Americas.