Philosophi疆 Naturalis Principia Mathematica, Latin for 'Mathematical Principles of Natural Philosophy', often referred to as simply the Principia, is a work in three books by Sir Isaac Newton, in Latin, first published 5 July 1687.

After annotating and correcting his personal copy of the first edition, Newton also published two further editions, in 1713 and 1726. The Principia states Newton's laws of motion, forming the foundation of classical mechanics, also Newton's law of universal gravitation, and a derivation of Kepler's laws of planetary motion (which Kepler first obtained empirically).

The Principia is 'justly regarded as one of the most important works in the history of science'.