Start with what "open" actually means for your course
The promise of open educational resources — OERs — is straightforward: materials that are free to access, and legally free to adapt. That second part is the one most instructors initially underestimate. A freely posted PDF that a publisher can take down next semester is not an OER. A true OER carries an open licence, most commonly from the Creative Commons suite, that explicitly grants permission to retain, reuse, revise, remix and redistribute. Before you invest time in building a course around any resource, check for that licence. If it isn't there, the material is free-to-read, not free-to-teach-with — a meaningful difference when your syllabus depends on it.
The licence tier matters too. A CC BY licence (attribution only) gives you the most flexibility: you can edit, excerpt and combine the work with other materials as long as you credit the source. A CC BY-NC-SA licence adds non-commercial and share-alike restrictions that won't affect most classroom use, but will constrain you if you want to package materials into something new. Reading the licence before you build saves headaches later.
Where to find materials worth building with
Good OER discovery takes about three places to check seriously.
Open textbooks are the load-bearing walls of most OER courses. The OpenStax catalogue, maintained by Rice University, covers introductory courses across the sciences, social sciences, humanities and business, with peer-reviewed texts that are regularly updated. The BCcampus OpenEd repository, based in British Columbia, holds hundreds of reviewed textbooks spanning disciplines from nursing to philosophy. Both are openly licensed (mostly CC BY, so check each title), downloadable in multiple formats, and printable at cost if students want paper. When you find a text that's eighty percent right for your course, the licence lets you strip, rearrange and annotate the remaining twenty percent rather than hunting for a perfect match that probably doesn't exist.
Subject repositories and archives fill the gap where no open textbook exists yet. arXiv holds preprints across physics, mathematics, computer science, economics and related fields; PubMed Central covers the biomedical and life sciences. These aren't textbooks — they're research articles, many deposited by authors exercising their green open access rights — but at upper-division and graduate level, reading real literature is often exactly what the course calls for. Zenodo, CERN's general-purpose repository, hosts datasets, presentations, working papers and multimedia alongside articles, making it unusually useful for courses that want students handling real research artefacts.
Open course collections provide syllabi, lecture notes and assessments you can adapt directly. MIT OpenCourseWare is the most extensive, covering thousands of courses with problem sets and exams under CC licences. The MERLOT repository aggregates peer-reviewed learning objects across higher education. The Open Education Consortium links to open courses from institutions worldwide. None of these replace your own teaching judgement, but they show how other instructors have structured similar material and what supplementary resources they found worth using.
Assembling it so it actually coheres
Finding materials is the easier half. The harder half is making a course from them feel like a course, not a playlist. A few principles help.
Map your learning outcomes first, then select materials — not the other way around. If you start with "this OpenStax chapter is pretty good," you'll drift. If you start with "students should be able to evaluate competing models of X," you'll select and adapt with purpose.
Version control matters. OERs are updated, links migrate, repositories occasionally retire items. Keep a local copy of anything critical and record the access date and URL in your course documentation. A stable DOI, where one exists, is more reliable than a bare web address — many repository-hosted materials carry one.
Attribute consistently and model good practice. Creative Commons licences require attribution, and showing students how you've credited sources in your own course materials quietly teaches citation norms alongside content. A short attribution line — title, author, licence, source — per adapted item takes seconds and demonstrates exactly what you'll eventually ask of them.
Patch gaps intentionally. Almost no OER-built course arrives complete from a single source. A common pattern is an open textbook for core content, a handful of arXiv or PubMed Central articles for current research, open datasets from Zenodo for applied work, and instructor-written bridging materials (released under CC BY themselves, to keep the whole thing remixable for colleagues). That last move — licensing your own additions openly — is how the OER ecosystem grows: the course you built becomes a starting point for the next instructor.