Watch the VIDEO. This presentation introduces how a relatively new, non-profit initiative – the Open Book Collective (OBC) – is furthering open science in a closing world via its diamond approach to funding open access (OA) book publishers. These range from small scholar-led publishers (e.g. Open Book Publishers, African Minds) to larger university presses (e.g. LSE Press, Leuven University Press). The OBC also addresses key gaps in the research infrastructures required for OA books to flourish, by providing funding to its service provider members (OAPEN, PKP, and Thoth Open Metadata). After this introduction, the presentation reports on a recently completed research project, led jointly by the Open Book Collective and Lancaster University, which explores the barriers standing in the way of the expansion of Diamond OA collective funding models in a European context. It explores the barriers standing in the way of the expansion of Diamond OA collective funding models in six European contexts, including two in Scandinavia: Finland and Sweden. This research involved in depth interviews with library representatives and other stakeholders to understand questions such as what existing collectively funded Diamond OA initiatives libraries already support, the policies that inform their support for OA books, the criteria used to assess Diamond OA initiatives, and the particular local and institutional challenges librarians confront in supporting Diamond OA. One key aim is of this research to answer the following question: how can libraries work to sustain a more equitable, sustainable and bibliodiverse OA future? For example, the report shows markedly different roles for the relationships between libraries and consortia within national contexts. In countries where Diamond OA support is led by a national consortium, librarians can feel less able to themselves lead on supporting new collective funding models, even if they support this work. The report also looks at the variations between libraries, especially regarding how responsibility for OA funding operates. For example, in some countries, OA leads within libraries are more likely to have dedicated OA budgets that they themselves control, whereas in other countries, the relevant budget lines tend to be more controlled by subject librarians, whose understanding of Diamond OA and its importance for the scholarly system can be lower than their OA lead colleagues. There are also recommendations for Diamond OA initiatives themselves, including the need to better understand the precise variations between different national and, in some cases, regional contexts.