The Cathedral and the Bazaar: Musings on Linux and Open Source by an Accidental Revolutionary is an essay, and later a book, by Eric S. Raymond on software engineering methods, based on his observations of the Linux kernel development process and his experiences managing an open source project, fetchmail. It examines the struggle between top-down and bottom-up design. The essay was first presented by Raymond at the Linux Kongress on May 27, 1997 in Würzburg (Germany) and was published as the second chapter of the same‑titled book in 1999.

Eric Steven Raymond, often referred to as ESR, is an American software developer, open-source software advocate, and author of the 1997 essay and 1999 book The Cathedral and the Bazaar. He wrote a guidebook for the Roguelike game NetHack. In the 1990s, he edited and updated the Jargon File, published as The New Hacker's Dictionary.