Open access infrastructure for books is becoming more mature, and it is being used by an in-creasing number of people. The growing importance of open access infrastructure leads to more interest in sustainability, governance and impact assessment. For this paper, we will assess the OAPEN Library. In the spring of 2022, it passed the milestone of 20,000 titles. This was a good moment to evaluate the core asset of the OAPEN Library: its collection.
The OAPEN Library contains freely accessible books and chapters, all of which have undergone external peer review. In other words, it functions as an academic library and in our assessment we should treat it as such. However, it is an online library and the limitations of physical books do not play a part. Shelf space is not to be considered.
More important is the question of how well the collection meets the needs of its users. The OAPEN Library sees global usage; the collection reflects this by offering titles in over 50 languages. The collection is not focused on a specific subject area, but the choice of medium — books and chapters, not journals and articles — is more strongly associated with the humanities and social sciences. It does not track its users, but the supporters of the OAPEN Libraries are globally dis-tributed academic institutions, scientific and scholarly funders and publishers. An assessment of the OAPEN Library should therefore take into account the diversity of languages, subjects and stakeholders.