Portions of the course material were adapted from Introduction to Probability (second edition) by Joseph K. Blitzstein and Jessica Hwang, Chapman & Hall/CRC Press (2019), ISBN 9781138369917, used with permission.
A free online version of the book (non-downloadable) is available at http://probabilitybook.net.
If you're interested in purchasing a print copy of the book, please visit the publisher's website (linked above) or Amazon.com.
Note: If you are following along with the book, the examples, figures, theorems, etc. may be numbered differently in edX than in the book. Refer to the information at the beginning of each unit to see which chapter or chapters it corresponds to in the book.