The first step to working with Open Educational Resources (OER) is finding appropriate ones to use.

On this page, we outline a general searching strategy, list a number of quality criteria you can use to judge the appropriateness of any found OER, and provide links to a number of webpages where you can find different types of OER.

Search strategy for finding OER

Before you can start using OER, you need to find them. There are over 2,000,000,000 works that have a Creative Commons license, so there is enough to use. Effectively searching for OER employs the same information literacy skills needed for effectively searching for relevant literature for research purposes. In its simplest form then, the order of operations when searching for OER is as follows:

1. Identify keywords

2. Search broadly (OER search engines + Google)

3. Start general and then get specific

4. Evaluate the sources

5. Curate the content you find

6. Reflect and repeat
    

Quality criteria for evaluating OER

As OER are often created by educators and students, and are more adaptable than traditional, copyright-protected educational materials, available OER can vary in their quality and usefulness. Therefore, it is important to take the time to critically evaluate any found OER before working with them. Some repositories or search engines provided quality criteria and rating systems, allowing users to leave a detailed review of an OER. However, it is always important to examine OER yourself to judge whether they are a good starting ground for your course.

Here, we consider a number of quality criteria you can use to evaluate your OER. These criteria are adapted from Module 7 of the finding Free and Open Resources tutorial of the University System of Georgia, licensed under a CC-BY 4.0 International License. These criteria have also been promoted by the City University of New York. For more information on the specific licenses, you can visit our guide on licensing and sharing your work.

When considering this list of criteria, there are two important aspects to remember. First, this list is not the comprehensive final set of criteria that every good OER needs to adhere to. Certain criteria may be less relevant given your course, or the specific type of OER you are looking for. Second, even if a found OER is not completely to your satisfaction with regards to important quality criteria, you can most likely adapt it to make it fit your specific needs. OER are not finished pieces, so remain flexible in your search. For more information on adapting the OER to your needs, you can see our guide on adapting and creating OER.

As there are tons of open works available online, there are also many sources to look for OER. Here we present the (in our view) best places to find (specific types of) OER. These lists are based on the full list found on our OER resource list pages. If you cannot find an appropriate OER in the resources listed here, we recommend visiting those pages.

Best general OER repositories and search engines

• Edusources - CC licenses - Repository for all types of OER from Dutch IT cooperation SURF. The University of Groningen posts their OER here first. Collection is steadily growing, has complete metadata per material, and easy license information
• City University of New York OpenED - CC licenses - CUNY's page on OER Commons. CUNY is a leader in OER field, and this provides a nice introduction to one of the biggest OER repository. Good metadata and license information
• OASIS - Varied - Polished search engine that searches through many other OER websites. Good filters for fine-tuning your results
• BC open collection by BCcampus - CC licenses - Fast website with many different types of OER, filters for easy searching, and good license information
• OER Commons - Varies - The staple OER repository. Beware that copyright-restricted, but free materials can also be posted here. Many fitlers and good license information
• Ontario Open Library - Open licenses (CC, GNU GPL) - Repository with different types of OER, a lot of H5P modules, and good metadata and license information
• GoOpenVA - CC licenses - Go Open VA's page on OER Commons. Has a smaller collection, whilst benefiting from the power of OER Commons
• MERLOT - Varied licenses - One of the biggest and well known repositories of OER. Be sure to check license information, as it also can contain copyrighted materials
• Open Research Library - CC licenses - OER repository with clear license information, good filters, and easy search options

Best general open (text)books and journal articles sources

• Openstax - CC BY, with some exceptions - Reviewed, high quality textbooks that have already been often used in teaching across the globe
• Figshare - CC licenses - Research output in the broadest sense, but a lot of articles generally. You can filter for CC licensed content
• Preprint Archive Service - Depends on resource, check license section - A central hub where many of the preprint archives (arXivs) can be searched, created by the well known Open Science Framework
• Milne Open Textbooks - CC licenses - Textbooks by the State University of New York (SUNY) Geneseo publishing house. Easy searching and professional online look
• Pressbooks Directory - CC licenses and Public Domain - Huge selection of high quality open textbooks, presented in a polished and interactive environment
• OAPEN - Filterable by CC license - Big selection of Open Access books and chapters. By filtering the search you can prevent finding incomplete records
• Manitoba Open Textbooks - CC licenses, and no ND - Simple and clean website to search for open and editable books
• Open Textbook Library - CC (no ND) and GNU GPL - A famous search engine for open textbooks, with a review system to see how other educators use the books
• Libretexts - CC BY-NC-SA unless otherwise stated - A multi-layered library that funnels you to the right book for your course
• intechOpen Books - CC BY and CC BY-NC - High quality, peer-reviewed books on many subjects  

Best open courses, courseware, and MOOC sources

• Open Course Library - CC BY - A link through page for courses saved in Google Drive with a permissive license. Some courses unfortunately require asking for access, and they are a bit old, but the drive environment is really useful
• Wolfram demonstrations project - CC BY-NC-SA - Interactive demonstrations and class activities for many subjects. Including full downloads and source code and good license information
• UCI Open - CC BY-SA - Full courses with lecture recordings (unfortunately YT, so not downloadable) and ancillary materials, all under a permissive license
• eCampus Ontario H5P catalog - CC and other open licenses - Huge collection of H5P modules, HTML-based inserts that you can use to make websites and online environments more interactive

Best open image sources

• Open Peeps - CC0 license - repository of cartoony drawings of customizable characters
• Openverse (formerly CC Search) - CC licensed or Public Domain - search engine for CC licensed or public domain images (and audio)
• Flickr Creative Commons - CC licensed or Public Domain - millions of images with clear license information
• UG Special Collections digital collections -  Public Domain and more - many images and scans of old (but also newer) unique documents in possession of the University of Groningen
• SVG Silh - CC0 license - SVG (vector) graphics with a clear, open license, and  that can be color edited on the website
• Reshot - Reshot free license (CC0-like) - many icons and vector drawings released with a very easy and clear license
• Centre for Ageing Better image library - CC0 - photos of the elderly engaging with society and each other
• Slide carnaval - CC BY - interesting slide designs for people looking to shake up their presentations
• ClipSafari - CC0 - vectors and clipart made available under an easy license
• Openclipart -  CC0 - clipart in the public domain
• xkcd - CC BY-NC - famous (sciency) comics, often with humorous twist
• Google Images - CC licensed content - by using tools > usage rights > Creative Commons licenses on the result page, you can find many openly licensed images
• Undraw - Undraw free license - drawn vector illustrations with a clear license, color customizable on the website
• Nappy - CC0 - photos featuring black and brown people that can be used to increase diversity in representation
• Pxhere - CC0 - Stock photo website with clear CC0 license and clear metadata
• Pexels - Pexels license - Easy to understand license, and the website is a staple in the field open images
• Unsplash - Unsplash license - Easy license, and high quality photos and images
• Pixabay - Pixabay license - Easy license, website has also videos, music and sound effects, which slightly hampers ease of use

If you already are using a textbook you really enjoy, you can use this tool by California State University to find free and open alternatives, or additional course materials related to it.

Some OER sources collect OER appropriate for specific fields. Like above, we present the best suggestions for sources to find subject-specific texts and courseware here, as well as the best sources to find open multimedia other than images.

These suggestions are based on the full lists found on our OER resource list pages. As these suggestions span multiple fields, it may be that a specific field is not presented in the top suggestions. If you cannot find an appropriate OER in the resources listed here, we recommend visiting the dedicated pages for the full lists.

STEM & Medicine: Best open texts & open courseware sources

• Freetechbooks - Open licenses, generally CC - Books and lecture notes with clear licensing, easy searching and downloading
• Light and Matter - CC BY-SA - Small, but impressive collection of books on physics and STEM in general with clear license
• American Institute of Mathematics - CC licenses, but also some just free - Curated list of open books on mathematics, with links on where to find them 

• Openlab at City Tech Bio OER - CC BY-NC-SA - Multimedia enhanced biology lessons/modules with a permissive license, as well as the syllabus for the course that used these modules. Also an interesting example of what you could make yourself, or ask students to make for a course
• PhET interactive simulations - CC BY - HTML5 based STEM simulations and teaching activities build around these simulations, all with a permissive license. Can be downloaded and embedded on websites for ease of use. Registration required to see activities
• TU Delft OpenCourseWare - CC BY-NC-SA - Open courses and course materials, as well as a link to MOOCs. High quality materials with a permissive license
• Open Education Resources for nursing - CC BY - Open online textbooks and (VR) nursing simulations in H5P, as well as lesson plans for these simulations. Comprehensive, although perhaps a little US focused
• Anatomy Tool - CC licenses - Anatomy and medicine simulations, quizzes and images by Dutch and Flemish universities
• Clinical Anatomy - CC BY-NC-SA - anatomy lessons, images and interactive simulations, all presented on an easy to use website

Arts, Humanities & Law: Best open texts & open courseware sources

• Pugetsound Music Theory - GNU Free Documentation License (CC BY-SA-esque) - Open (text)book and exercises on music theory. Website unfortunately has unsafe connection, but the material is detailed and has a good license
• Avalon Project - Free, likely Public Domain - Web versions of important historical, political, and law documents. License information is unfortunately missing, but due to age and type of documents is likely Public Domain
• E-international Relations Books - CC BY-NC - Impressive collection of international relations books with a good license, but lacking modifiable formats, and hosted on a website with some intrusive ads

• Excelsior Online Writing Lab (OWL) - CC BY - Comprehensive, and permissively licensed resource for academic writing and reading

Social Sciences & Business: Best open texts & open courseware sources

• EconBiz - Open Access - Search engine for journals, working papers & conferences in Business & Economics. Useful for researchers and students
• Lyryx Open Textbooks - CC By or BY-NC-SA - High quality, peer reviewed books on business, economics and mathematics. Getting tot hem may require signing up, but the books can be found through other platforms such Open Textbook library
• NOBA Project - CC BY-NC-SA - 105 modules on different psychology topics that you can customize into your own textbook. Written by experts in the field, and with a permissive license. Do need to sign up and log in 

• SDG academy - CC BY-NC-SA - Videos on the Sustainable Development Goals. Good license, interesting topic, and easy options to download
• QuantEcon -  CC BY-SA for the lectures - Coding lectures and code for economic analysis and modeling. Comprehensive and easy to use

Open audio and video sources

• Free Music public Domain - CC BY - Free music for videos and other educational projects. If you want to use it for business (non-educational) purposes, you need to pay. Built-in license generator
• Free Music Archive (FMA) - CC licenses and public domain - Filter for open songs. Easy to search, but does requiring signing up
• Youtube Audio Library (CC tracks) - CC BY - Lots of songs that can be directly used for Youtube videos, but also downloaded for use elsewhere
• Josh Woodward Songs - CC BY - Collection of albums and songs in different styles. Easy license and clear website

• Youtube - CC BY - Tons of materials that you can use in class, er easily embed in online learning environments (which is allowed). You can also filter for CC BY videos that you can reuse and alter.
• Videvo - CC BY & Videvo attribution license - Stock footage website with easy licenses and easy searching
• Videezy - Videezy standard license (attribution) - Stock footage website with easy license

With the information in this guide, we hope you are now able to search for and critically evaluate a range of OER. If you need more support or have questions regarding searching for and evaluating OER, you can reach the OER support services at: oer-library@rug.nl.

In our other guides, we outline what OER are, how copyright is related to OER, reasons for why OER can/should be used in teaching, how you can implement any found OER in your teaching, how you can create your own OER, and how you can share your own work as an OER with the world.