The purpose of this paper is to determine how the I-Share collection serves its members, focusing on the state-wide use of I-Share domestic monographs (2003-2008) by subject, collection overlap (number of copies owned), publisher, and how frequently books by subject are being used and to make recommendations for future selection criteria. Illinois is fortunate to have the CARLI (College and Research Libraries in Illinois) consortium which manages “I-Share,” a 76-member shared online catalog equipped with patron-initiated borrowing using the Voyager system. I-Share successfully circulates hundreds of thousands of books annually among these libraries, dramatically broadening the scope of each member’s collection. Results found that numbers of copies purchased by I-Share and use/circulation fell into three categories: high overlap with a corresponding high use, low overlap with a corresponding low use, and a middle area with a high number of copies with low to middle use. Additional analyses by publisher and Library of Congress subject classification were also conducted. The study also allowed for a comparison of what was purchased versus what was available for purchase as represented by the database of a large monograph vendor.