OER Knowledge CloudJournal ArticleWalters, William H.Although Open Educational Resources (OERs) can help reduce costs and maximize access to instructional materials, academics face significant problems in identifying good OER textbooks. This can be traced, in part, to the low quality of many OER directories. This study evaluated more than 350 potentially relevant resources, identifying 95 multidisciplinary and 23 subject-limited OER directories that include a relatively high proportion of free textbooks rather than other OERs (syllabi, assessment materials, etc.). Comparative information is presented for each of the 118 directories, with special attention to those with high recall, high precision, explicit and meaningful selection criteria, and consistently good textbook quality. The results focus on the characteristics of the OER directories, the extent to which they support the discovery of textbooks, the particular directories that are likely to be most useful, and the ways in which the most useful directories are systematically different from the others. There are at least 24 high-quality OER directories, but three—the Open Textbook Library, the B.C. Open Collection, and LibreTexts Commons—are especially useful. By devoting more attention to directories such as these, we can overcome the greatest barrier to the adoption of OER textbooks—the difficulty of identifying titles that can replace conventional texts.20242024/10/04EnglishPublications12432United States10.3390/publications12040032https://www.mdpi.com/2304-6775/12/4/322304-6775yesdirectoriesguidesOEROpen AccessOpen Educational Resourcestextbookshttps://www.mdpi.com/2304-6775/12/4/32publications-12-00032-v2.pdfUnited States, North America