E-books constitute major challenges for library collections generally and present fundamental problems for consortial collection development specifically. The Triangle Research Libraries Network (TRLN) and Oxford University Press (OUP) have created a mutually equitable and financially sustainable model for the consortial acquisition of e-books coupled with print titles needed to support instruction and research across the disciplinary spectrum within a transitional framework that is acceptable to users while moving both libraries and publishers to a decidedly electronic environment for monographs. Working with YBP Library Services, TRLN and OUP developed a flexible vending model for systematically increasing e-books acquisitions in tandem with reducing print intake over time and keeping net costs constant that other consortia and publishers would find useful. This article focuses on creating an acceptable and sustainable model that allows libraries to shift to e-books and the implications for traditional cooperative collection development. The research reports on the principles undergirding the pilot, how it developed, challenges encountered and lessons learned, librarian and user reactions to this format shift, and resulting philosophical and practical evolutions in consortial approaches to monographic acquisitions and understandings of what constitutes cooperative collections success in a digital environment. Contains notes.