Eduard Rudolf Thurneysen (March 14, 1857 – 9 August 1940) was a Swiss linguist and Celticist.
Born in Basel, Thurneysen studied classical philology in Basel, Leipzig, Berlin and Paris. His teachers included Ernst Windisch and Heinrich Zimmer. He received his promotion (approximating to a doctorate) in 1879 and his habilitation, in Latin and the Celtic languages, followed at the University of Jena in 1882.
From 1885 to 1887 he taught Latin at Jena, then taking up the Chair of Comparative Philology at the University of Freiburg where he replaced Karl Brugmann, a renowned expert in Indo-European studies.
In 1909 Thurneysen published his Handbuch des Alt-Irischen, translated into English as A Grammar of Old Irish by D. A. Binchy and Osborn Bergin, and still in print as of 2006. In 1913 he moved to the University of Bonn. It is in this period that Thurneysen has been called the greatest living authority on Old Irish.
He retired in 1923 and died in Bonn in 1940. The Rudolf Thurneysen Memorial Lecture (German: Vortrag in Memoriam Rudolf Thurneysen), given at Bonn, is named in his honour.