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.
He is editor-in-chief of the Journal of Graph Theory and the Electronic Journal of Combinatorics, and editor of Combinatorica, the Journal of Combinatorial Theory, Ser B, Discrete Mathematics, and the European Journal of Combinatorics.
He was awarded the Dedicatory Award of the 6th International Conference on the Theory and Applications of Graphs by the Western Michigan University in May 1988, the Lester R. Ford Award by the Mathematical Association of America in 1993, and the Faculty of Mathematics Alumni Achievement Medal by the University of Waterloo in 2005. He was included on the ISI Web of Knowledge list of the 250 most cited mathematicians.