The Directory of Open Access Books (DOAB) is a service of the OAPEN Foundation, an international initiative dedicated to open access monograph publishing, based at the National Library in The Hague. Its primary aim is to increase the discoverability of academic, peer-reviewed open access books. Its repository links to more than 13,000 books and chapters from 285 publishers. 

In partnership with BCcampus, eCampusOntario's repository contains over 250 open textbooks aligned with the top 40 highest-enrolled subject areas in the province. 

Rice University's OpenStax hosts a repository of introductory university-level open textbooks. OpenStax textbooks can be adapted and modified to an instructor's requirements.

The Open Textbook Project, an initiative of BCcampus, provides a range of open textbooks in an effort to reduce student costs.  The BC Open Textbook collection is based on the top 40 first and second-year enrolled courses at public postsecondary institutions in British Columbia.

The University of Minnesota's Open Textbook Library brings together the open textbook repositories of nine postsecondary institutions. You can browse subjects in accounting & finance, business, management & marketing, computer science & information systems, economics, general education, humanities & language, law, mathematics & statistics, natural & physical sciences, and social sciences. 

Interdisciplinary and ranging from preschool to graduate level education, OER Commons is a dynamic digital library and network. Explore over 50,000 high-quality open education materials such as full university courses, interactive mini-lessons and simulations, open textbooks, adaptations of existing open work, and K-12 lessons plans worksheets and activities.