Carsten Thomassen (born August 22, 1948 in Grindsted) is a Danish mathematician.
He has been a Professor of Mathematics at the Technical University of Denmark since 1981, and since 1990 a member of the Royal Danish Academy of Sciences and Letters.
His research concerns discrete mathematics and more specifically graph theory.
In 1990, he was an invited speaker (Graphs, random walks and electric networks) at the ICM in Kyōto.
He was included on the ISI Web of Knowledge list of the 250 most cited mathematicians.