IJsewijn (Zwijndrecht, 30 December 1932 – Leuven, 27 November 1998) was a Belgian Latinist.
He studied classical philology at the Katholieke Universiteit Leuven, where he became a professor in 1967.
An authority on Neo-Latin literature (Latin texts since the beginning of humanism in the 14th century), IJsewijn has been called "the founding father of modern neo-Latin studies".
In 1980, he was awarded the Francqui Prize on Human Sciences.
A collection of essays in his memory was published in 2000.