The Open Textbook Library (OTL) contains 400+ open textbooks. Faculty from a variety of colleges and universities review OTL textbooks to assess their quality and suitability for teaching. All OTL books can be read online and freely downloaded, and printed cheaply. They are either used at multiple higher ed institutions, or affiliated with an institution, scholarly society, or professional organization.
Looking for more resources? Find full courses, lesson plans, videos, tests, software, books, or images in these repositories: