As of August 2025, there are two separate editions of Active Calculus – Single Variable. The first edition is the long-standing one that has been available from this site since 2018, whose last major update was August 2019; the second edition was published in early August 2025.
You can learn more about the second edition of AC-single in this recent blog post and see a summary of the differences between the first and second editions on this separate page.
In addition to the textbooks themselves, we offer a wide range of ancillary materials for instructors. Learn more about each text via links in the main menu above, including information about free PDF version and how to purchase print copies (of the first editions). Each book is freely available in HTML (that can even be read on a smartpone); follow the links in the menu above to each edition’s dedicated page at activecalculus.org/acs1e/ and activecalculus.org/acs2e/.
 |  |
A print version and new cover image for the 2nd edition of ACS are forthcoming and will be available by January 2026. On the respective landing pages, you’ll see “1e” and “2e” to clarify which edition is being considered, and the two different cover images are used to distinguish between the editions.
Each text still carries a Creative Commons BY-SA license that allows users to clone, fork, and modify the GitHub source, provided they give attribution and share the results of their work freely. The GitHub source points to 2e, and from August 2025 forward, only the 2e source will be updated.
In Fall 2023, we posted a draft of a new chapter 8 (then called “8a”) that has become canonical in the 2nd edition. If you happen to be still using that HTML (only) version, it remains available via https://activecalculus.org/acs-8a/.
