Georg Joachim von Lauchen, also known as Rheticus (16 February 1514 – 4 December 1574), was a mathematician, cartographer, navigational-instrument maker, medical practitioner, and teacher.

He is perhaps best known for his trigonometric tables and for being Nicolaus Copernicus' sole pupil, who facilitated the publication of Copernicus' De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres).