Joseph Adolphe François Thas (born 13 October 1944, Dilbeek, Belgium) is a Belgian mathematician, who works on combinatorics, incidence geometry and finite geometries.
Thas received in 1969 his PhD from Ghent University under Julien Bilo with thesis Een studie betreffende de projective rechte over de totale matrix algebra
M
3
(
K
)
{\displaystyle M_{3}(K)}
der 3x3-matrices met elementen in een algebraïsch afgesloten veld K.
Thas showed how to extend projective geometry and cross-ratios with the concept of a projective line over a ring.Thas is an emeritus professor at Ghent University.