From an ebrary Announcement:
The Boston Library Consortium (BLC) has partnered with ebrary and YBP Library Services (YBP), to make it easier and more affordable for its member libraries to acquire authoritative e-books from publishers including Princeton University Press, Wiley, and Brill. Participating BLC member libraries are now offering seamless access to titles eligible for Consortium-wide purchasing automated through YBP. In the patron/demand-driven acquisition model, titles are only purchased based on real usage from the end-user.
Students and faculty from participating BLC members are now able to select and identify titles for their access, while the Consortium makes the actual purchase. Access to purchased titles is shared among all participating members and those member libraries that already have patron driven acquisition with ebrary can continue to run individual programs.