This paper offers seven things one should know about open textbook publishing. These seven facts are: (1) The open educational resources model, including textbooks, has emerged as a response to rising text prices, a need for greater access to high-quality learning materials, the proliferation of e-reader devices, and a trend in publishing toward electronic media; (2) Those who create or contribute to open textbooks are often motivated by the conviction that content--particularly for educational purposes--should be open; (3) Many open texts are available from for-profit publishers; (4) Open resources can promote active learning through student interaction with the text, particularly when they contribute to authorship; (5) An open text may seem to be missing an essential credential that speaks to its validity; (6) Open publication may encourage commercial publishers to provide additional services; and (7) Instructors can design content for their courses on an as-needed basis, choosing from an array of books, articles, videos, audio recordings, and readings.