Textbooks in the Open Textbook Library are considered open because they are free to use and distribute, and are licensed to be freely adapted or changed with proper attribution. The criteria for including new textbooks in the Open Textbook Library are:

• All content must be openly licensed. We accept textbooks licensed with GNU and Creative Commons (CC) licenses, with the exception of the CC ND (No Derivatives) component. CC BY is recommended. Go to Creative Commons for more information about selecting a license for your work.
• Must be a complete textbook available as a complete portable file (e.g. PDF, EPUB).
• Must be in use at multiple higher education institutions, or affiliated with a higher education institution, scholarly society, or professional organization.
• Must be an original textbook (not a derivative of another textbook). Possible exceptions to this criteria are modifications that reflect the needs or context of an entirely new audience. For example, the textbook has been changed in such a significant way that it is now relevant to a new country, profession, or has been translated into a new language. Authors or publishers will be asked to demonstrate significant changes to the original text.