Below are selected Open Educational Resources (OER) in math, with an emphasis on resources used by other Iowa colleges/universities as well as textbooks reviewed in the Open Textbook Library or by relevant associations. Some free resources may be included that aren't technically OER because they do not have open licenses. Be sure to evaluate each resource for quality and usage rights.
For all Open Textbook Library titles in math, see https://open.umn.edu/opentextbooks/subjects/mathematics.
For more textbooks & other resources, use the Open Textbooks and Search tabs on the left side of this guide. Rod Library's OneSearch also includes some open textbooks as well as licensed ebooks; note that if you plan to use a library-licensed ebook for a course, you need to notify your liaison librarian well in advance (more on textbooks & library ebooks).