"OER are education materials that are shared at no cost with legal permissions for the public to freely use, share, and build upon the content. [..] For a resource to be an OER – it has to (a) be available to everyone at no cost and (b) be in the public domain or under an open license that gives everyone 5 Rs legal permissions to modify the resource." /Creative Commons

Finding OERs

You can find OERs by searching on the Internet. The easiest way to verify that an educational resource qualifies as an open educational resource, granting you the 5R permissions, is by making sure the resource is either in the public domain or has been licensed under a Creative Commons license that allows the creation of derivative works—such as CC0, – CC BY, CC BY-SA, CC BY-NC, or CC BY-NC-SA.

Below some links where you can find different materials:

Open textbooks: OpenStax, the Open Textbook Library or BCcampus Open Education.
Open Courseware: Open Education Consortium, the ProEVA at the University of the Republic of Uruguay (UDELAR), or MIT OCW

Learn more

(5.1 OER, Open Textbooks, and Open Courses | Creative Commons
Creative Commons for Educators and Librarians/Chapter 5
Understanding OER – Open Educational Resources: Basics & Beyond

Finding, and creating OER

This video by TheOGTepository is shared under CC BY

Information about finding resources by Creative Commons is shared under CC BY 4.0