The first thing to recognise when talking about finding open resources is that, like any research activity, it will take time and persistence to accomplish and will be more difficult at first until you develop some experience with this activity.
It may be easier to identify the problem you would like to solve first rather than wade into a sea of websites and repositories. Do you want to find an open textbook to replace a costly commercial textbook? Or do you want to find an open data set for students to analyse as part of an assessment? Having this kind of focus for your search may make things easier.
Another thing to recognise is that others can aid you in your search for appropriate open resources. We recommend you make contact with a librarian in your institution who will be able to advise and guide you to the best resources. Talk to colleagues to see if they have found open resources similar to what you are searching for.
Having identified your goal and getting any guidance you can, you need to begin locating and exploring websites and repositories, keeping track of your efforts. Early explorations will give you an overview of the type of content you can find in such locations. It is a good idea to begin searching broadly before narrowing your search.
Mason OER Metafinder - The Mason OER Metafinder runs a simultaneous real-time federated search across 22 different OER sources.
OASIS - Openly Available Sources Integrated Search (OASIS) is a search tool that aims to make the discovery of open content easier. OASIS currently searches open content from 117 different sources and contains 388,707 records.
Openstax College - Initiated by Rice University, their free textbooks are developed and peer-reviewed to ensure they meet college courses' scope and sequence requirements.
Open Textbook Library - Created by the University of Minnesota to support the development of high-quality open textbooks in various subjects.
CC Search - CC Search is a tool that allows openly licensed and public domain works to be discovered and used by everyone.
There are numerous OER textbook platforms available; some of the more well-known ones are:
BC Campus OpenEd - Provision of openly licensed textbooks and other OER materials with a broad discipline focus, including; business, education, science and mathematics
EdTech Books - Provision of openly licensed textbooks and other OER materials focusing on education as a discipline.
Lumen Learning - Lumen provides open courses in a variety of high-demand subjects and disciplines. These courses are collections of high-quality OER and may not necessarily be textbooks.
Merlot - A curated collection of free and open online teaching and learning services.
OER Commons - Provides college-level open textbooks from higher education institutions around the world.
Teaching Commons - The Teaching Commons showcases high-quality open educational resources from leading colleges and universities and makes them available to educators and students around the world.