Several libraries have become active partners in Open Access publishing of books in the Humanities and Social Sciences (HSS). Not only have libraries started up their own presses, they are also collaborating with existing presses or forming alliances with other institutions on campus such as scholarly communication offices, ICT departments, and academic research centers. By combining institutional strengths and enabling the sharing of resources across institutions, these collaborations offer synergies and efficiencies in the scholarly book publishing business. This paper examines this new function taken on by libraries. Using research conducted by the European project “Open Access Publishing in European Networks” (OAPEN) on OA publishing models and business models for books, we look at libraries’ motives and challenges and explore how their new roles enable them to serve their customers in the most effective way. By combining digital repositories with scholarly publishing, libraries can facilitate and support HSS book publishing and can help sustain the scholarly monograph in the transition towards digital formats and an Open Access future.