Unlike commercial publishers, who work hard to get rid of older editions of their books in order to make professors make students buy the latest edition, our open-source philosophy means that we maintain prior editions indefinitely. We definitely recommend using the most recent edition and are transparent about changes, but if you ever really need to see what was in an older edition, you can find a link here. (Older print editions may be discontinued, but if you really need one, please contact us.)

• 2017.2 Edition. Released in HTML, Kindle, and EPUB (Apple Books pending; other EPUB marketplaces; not available through Barnes & Noble). Changes from the 2017.1 Edition are on the Errata page.
• 2017.1 Edition. Released in HTML only and will remain the current edition for the 2020–2021 academic year. Changes from the 2017 Edition are on the Errata page. HTML remains available online.
• 2017 Edition: This is the most recent edition for print and PDF and will remain the current edition of these formats for the 2021–2022 academic year. Please see Get the Book for more information. HTML remains available online.
• 2016.1 Edition: Released in HTML only. Remains available online.
• 2016 Edition: Available in HTML and PDF. The print version is no longer available.