Principia Discordia is a Discordian religious text written by Gregory Hill (Malaclypse the Younger) and Kerry Wendell Thornley (Omar Khayyam Ravenhurst). It was originally published under the title "Principia Discordia or How The West Was Lost" in a limited edition of 5 copies in 1965. The name, meaning "The Principles of Strife", probably deviates from correct Latin which would read Principia Discordiæ, though "Discordia" might be taken as an adjective (analogous to the title of Russel's and Whitehead's Principia Mathematica), thus Principia Discordia would mean something along the lines of "Discordian/Strife-ish Principles".
There have been multiple subsequent editions of the text, some of which have been heavily modified from the original. The first widely available and most well-known edition was published by Loompanics Unlimited in 1980, under the title Principia Discordia, Or, How I Found Goddess and What I Did to Her When I Found Her: The Magnum Opiate of Malaclypse the Younger. This edition substantially updates the text, removing several sections from previous editions, and adding a substantial amount of additional text. A subsequent edition was published by Steve Jackson Games in 1994, under the title Principia Discordia or, How I Found Goddess, and What I Did to Her When I Found Her, The Magnum Opiate of Malaclypse the Younger, wherein is explained Absolutely Everything Worth Knowing About Absolutely Anything; and includes additional modifications and added text.
It is a common misconception that the Principia Discordia is based on snippets and quotes given in the Illuminatus! Trilogy, instead Wilson and Shea belonged to the original Discordian circle and had access to the book.