Paul Guldin (original name Habakkuk Guldin) (June 12, 1577 - November 3, 1643) was a mathematician and astronomer. He discovered the Guldinus theorem to determine the surface and the volume of a solid of rotation . This theorem is also known as Pappus-Guldinus theorem and Pappus's centroid theorem, attributing Pappus of Alexandria.

He was born in St. Gallen, Switzerland and was a professor of mathematics in Graz and Vienna.