Ludolph van Ceulen (German: [ˈluːdɔlf fan ˈkɔʏlən], Dutch: [ˈlydɔl(ə) fɑŋ ˈkøːlə(n)]; 28 January 1540 – 31 December 1610) was a German-Dutch mathematician from Hildesheim.

[1] In 1600 he was appointed the first professor of mathematics at the Engineering School, Duytsche Mathematique, established by Maurice, Prince of Orange, at the relatively new Leiden University.

He shared this professorial level at the school with the surveyor and cartographer, Simon Fransz van Merwen [nl], which shows that the intention was to promote practical, rather than theoretical instruction.

Theological professors generally believed that practical courses were not acceptable studies for a university, but they were not willing to reject the School outright since it was founded by Prince Maurice.

Ludolph van Ceulen spent a major part of his life calculating the numerical value of the mathematical constant π, using essentially the same methods as those employed by Archimedes some seventeen hundred years earlier.