Philosophiae Naturalis Principia Mathematica, Isaac Newton's three-volume work containing explanations of his laws of motion and his law of universal gravitation.

Principia Mathematica, Alfred North Whitehead and Bertrand Russell's axiomatic work on mathematics.

Principia Discordia, a major holy book in Discordianism.

Principia Ethica, a seminal work in metaethics by G. E. Moore.

The Principia, a religion-based preschool, gradeschool, boarding highschool, and college.