The Cathedral and the Bazaar

Eric Steven Raymond

This is version 3.0


Permission is granted to copy, distribute and/or modify this document under the terms of the Open Publication License, version 2.0.

$Date: 2002/08/02 09:02:14 $

Revision History
Revision 1.5711 September 2000esr
New major section ``How Many Eyeballs Tame Complexity''.
Revision 1.5228 August 2000esr
MATLAB is a reinforcing parallel to Emacs. Corbatoó & Vyssotsky got it in 1965.
Revision 1.5124 August 2000esr
First DocBook version. Minor updates to Fall 2000 on the time-sensitive material.
Revision 1.495 May 2000esr
Added the HBS note on deadlines and scheduling.
Revision 1.5131 August 1999esr
This the version that O'Reilly printed in the first edition of the book.
Revision 1.458 August 1999esr
Added the endnotes on the Snafu Principle, (pre)historical examples of bazaar development, and originality in the bazaar.
Revision 1.4429 July 1999esr
Added the ``On Management and the Maginot Line'' section, some insights about the usefulness of bazaars for exploring design space, and substantially improved the Epilog.
Revision 1.4020 Nov 1998esr
Added a correction of Brooks based on the Halloween Documents.
Revision 1.3928 July 1998esr
I removed Paul Eggert's 'graph on GPL vs. bazaar in response to cogent aguments from RMS on
Revision 1.31February 10 1998 esr
Added ``Epilog: Netscape Embraces the Bazaar!''
Revision 1.29February 9 1998esr
Changed ``free software'' to ``open source''.
Revision 1.2718 November 1997esr
Added the Perl Conference anecdote.
Revision 1.207 July 1997esr
Added the bibliography.
Revision 1.1621 May 1997esr
First official presentation at the Linux Kongress.


I anatomize a successful open-source project, fetchmail, that was run as a deliberate test of the surprising theories about software engineering suggested by the history of Linux. I discuss these theories in terms of two fundamentally different development styles, the ``cathedral'' model of most of the commercial world versus the ``bazaar'' model of the Linux world. I show that these models derive from opposing assumptions about the nature of the software-debugging task. I then make a sustained argument from the Linux experience for the proposition that ``Given enough eyeballs, all bugs are shallow'', suggest productive analogies with other self-correcting systems of selfish agents, and conclude with some exploration of the implications of this insight for the future of software.

Table of Contents

The Cathedral and the Bazaar
The Mail Must Get Through
The Importance of Having Users
Release Early, Release Often
How Many Eyeballs Tame Complexity
When Is a Rose Not a Rose?
Popclient becomes Fetchmail
Fetchmail Grows Up
A Few More Lessons from Fetchmail
Necessary Preconditions for the Bazaar Style
The Social Context of Open-Source Software
On Management and the Maginot Line
Epilog: Netscape Embraces the Bazaar

Linux is subversive. Who would have thought even five years ago (1991) that a world-class operating system could coalesce as if by magic out of part-time hacking by several thousand developers scattered all over the planet, connected only by the tenuous strands of the Internet?

Certainly not I. By the time Linux swam onto my radar screen in early 1993, I had already been involved in Unix and open-source development for ten years. I was one of the first GNU contributors in the mid-1980s. I had released a good deal of open-source software onto the net, developing or co-developing several programs (nethack, Emacs's VC and GUD modes, xlife, and others) that are still in wide use today. I thought I knew how it was done.

Linux overturned much of what I thought I knew. I had been preaching the Unix gospel of small tools, rapid prototyping and evolutionary programming for years. But I also believed there was a certain critical complexity above which a more centralized, a priori approach was required. I believed that the most important software (operating systems and really large tools like the Emacs programming editor) needed to be built like cathedrals, carefully crafted by individual wizards or small bands of mages working in splendid isolation, with no beta to be released before its time.

Linus Torvalds's style of development—release early and often, delegate everything you can, be open to the point of promiscuity—came as a surprise. No quiet, reverent cathedral-building here—rather, the Linux community seemed to resemble a great babbling bazaar of differing agendas and approaches (aptly symbolized by the Linux archive sites, who'd take submissions from anyone) out of which a coherent and stable system could seemingly emerge only by a succession of miracles.

The fact that this bazaar style seemed to work, and work well, came as a distinct shock. As I learned my way around, I worked hard not just at individual projects, but also at trying to understand why the Linux world not only didn't fly apart in confusion but seemed to go from strength to strength at a speed barely imaginable to cathedral-builders.

By mid-1996 I thought I was beginning to understand. Chance handed me a perfect way to test my theory, in the form of an open-source project that I could consciously try to run in the bazaar style. So I did—and it was a significant success.

This is the story of that project. I'll use it to propose some aphorisms about effective open-source development. Not all of these are things I first learned in the Linux world, but we'll see how the Linux world gives them particular point. If I'm correct, they'll help you understand exactly what it is that makes the Linux community such a fountain of good software—and, perhaps, they will help you become more productive yourself.