A few years ago, when I wanted to explain why I believed that distributed revision control is important, the field was then so new that there was almost no published literature to refer people to.

Although at that time I spent some time working on the internals of Mercurial itself, I switched to writing this book because that seemed like the most effective way to help the software to reach a wide audience, along with the idea that revision control ought to be distributed in nature. I publish the book online under a liberal license for the same reason: to get the word out.

There's a familiar rhythm to a good software book that closely resembles telling a story: What is this thing? Why does it matter? How will it help me? How do I use it? In this book, I try to answer those questions for distributed revision control in general, and for Mercurial in particular.

By purchasing a copy of this book, you are supporting the continued development and freedom of Mercurial in particular, and of open source and free software in general. O'Reilly Media and I are donating my royalties on the sales of this book to the Software Freedom Conservancy (http://www.softwarefreedom.org/) which provides clerical and legal support to Mercurial and a number of other prominent and worthy open source software projects.

This book would not exist were it not for the efforts of Matt Mackall, the author and project lead of Mercurial. He is ably assisted by hundreds of volunteer contributors across the world.

My children, Cian and Ruairi, always stood ready to help me to unwind with wonderful, madcap little-boy games. I'd also like to thank my ex-wife, Shannon, for her support.

My colleagues and friends provided help and support in innumerable ways. This list of people is necessarily very incomplete: Stephen Hahn, Karyn Ritter, Bonnie Corwin, James Vasile, Matt Norwood, Eben Moglen, Bradley Kuhn, Robert Walsh, Jeremy Fitzhardinge, Rachel Chalmers.

I developed this book in the open, posting drafts of chapters to the book web site as I completed them. Readers then submitted feedback using a web application that I developed. By the time I finished writing the book, more than 100 people had submitted comments, an amazing number considering that the comment system was live for only about two months towards the end of the writing process.

I would particularly like to recognize the following people, who between them contributed over a third of the total number of comments. I would like to thank them for their care and effort in providing so much detailed feedback.

Martin Geisler, Damien Cassou, Alexey Bakhirkin, Till Plewe, Dan Himes, Paul Sargent, Gokberk Hamurcu, Matthijs van der Vleuten, Michael Chermside, John Mulligan, Jordi Fita, Jon Parise.

I also want to acknowledge the help of the many people who caught errors and provided helpful suggestions throughout the book.

Jeremy W. Sherman, Brian Mearns, Vincent Furia, Iwan Luijks, Billy Edwards, Andreas Sliwka, Paweł Sołyga, Eric Hanchrow, Steve Nicolai, Michał Masłowski, Kevin Fitch, Johan Holmberg, Hal Wine, Volker Simonis, Thomas P Jakobsen, Ted Stresen-Reuter, Stephen Rasku, Raphael Das Gupta, Ned Batchelder, Lou Keeble, Li Linxiao, Kao Cardoso Félix, Joseph Wecker, Jon Prescot, Jon Maken, John Yeary, Jason Harris, Geoffrey Zheng, Fredrik Jonson, Ed Davies, David Zumbrunnen, David Mercer, David Cabana, Ben Karel, Alan Franzoni, Yousry Abdallah, Whitney Young, Vinay Sajip, Tom Towle, Tim Ottinger, Thomas Schraitle, Tero Saarni, Ted Mielczarek, Svetoslav Agafonkin, Shaun Rowland, Rocco Rutte, Polo-Francois Poli, Philip Jenvey, Petr Tesałék, Peter R. Annema, Paul Bonser, Olivier Scherler, Olivier Fournier, Nick Parker, Nick Fabry, Nicholas Guarracino, Mike Driscoll, Mike Coleman, Mietek Bák, Michael Maloney, László Nagy, Kent Johnson, Julio Nobrega, Jord Fita, Jonathan March, Jonas Nockert, Jim Tittsler, Jeduan Cornejo Legorreta, Jan Larres, James Murphy, Henri Wiechers, Hagen Möbius, Gábor Farkas, Fabien Engels, Evert Rol, Evan Willms, Eduardo Felipe Castegnaro, Dennis Decker Jensen, Deniz Dogan, David Smith, Daed Lee, Christine Slotty, Charles Merriam, Guillaume Catto, Brian Dorsey, Bob Nystrom, Benoit Boissinot, Avi Rosenschein, Andrew Watts, Andrew Donkin, Alexey Rodriguez, Ahmed Chaudhary.

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