Open education resources (OER) are materials for teaching or learning that are ALWAYS free to use, adapt, and share. OER can include textbooks, courses, multimedia, data, and supplementary materials. (Tip: If you're brand new to OER, check out the Faculty OER Toolkit from BCampus.)
There are MANY places online where you can find OER. Below are some best bets, plus a tool for searching across multiple OER sites at once.
OER Metafinder: A one-stop shop for searching across multiple OER repositories.