APA (7th ed.) Citation

Williams, S. (2002). Free as in freedom: Richard Stallman's crusade for free software. O'Reilly.

Chicago Style (17th ed.) Citation

Williams, Sam. Free as in Freedom: Richard Stallman's Crusade for Free Software. Sebastopol, Calif.: O'Reilly, 2002.

MLA (9th ed.) Citation

Williams, Sam. Free as in Freedom: Richard Stallman's Crusade for Free Software. O'Reilly, 2002.