Using Open Education Resources is one way of creating Zero Textbook Cost courses.
OER textbooks and materials are freely and openly available to everyone to retain, reuse, revise, remix, and redistribute.
ZTC courses can include materials that are not open (so they can’t be modified). Examples of these could include articles, documents, films, and more accessed through databases at the VVC Library or other subscriptions paid through the college but are free for students.
More examples of ZTC resources:
Faculty & Systems Librarian
"'Open Educational Resources' are high-quality teaching, learning, and research resources that reside in the public domain or have been released under an intellectual property license, such as a Creative Commons license, that permits their free use and repurposing by others, and may include other resources that are legally available and free of cost to students. 'Open educational resources' include, but are not limited to, full courses, course materials, modules, textbooks, faculty-created content, streaming videos, tests, software, and any other tools, materials, or techniques used to support access to knowledge."
Section 67423 of the California Education Code (College Textbook Affordability Act of 2015)
Also see: SB-1359 Public postsecondary education: course materials.
Compelling Reasons to Consider OER – The Barriers