This article considers John Dee’s famous classification and justification of ‘the Sciences, and Artes Mathematicall’ in his Mathematicall praeface to Henry Billingsley’s Elements of geometrie of Euclid of Megara (1570), the first English translation of Euclid. It is a revised version of a lecture presented to the British Society for the History of Mathematics Autumn Meeting, October 2010, under the title ‘John Dee and the Elizabethan Mathematics of Everything’.