In September 2007, Yale University Library (YUL) and Microsoft agreed to partner in a large-scale project to digitize 100,000 books from the YUL collections--an ambitious effort that would substantially increase the library's digitized holdings, particularly in the area of its own text collections. YUL has been digitizing materials from its collections for many years, primarily in the area of visual art materials and slides, some specific textual materials, and a small number of books in need of preservation. However, YUL had yet to undertake an effort to digitize a major portion of its book collection. This article presents an analysis of YUL's special needs regarding mass digitization, illustrate the workflows and in-house technical developments necessary for mass digitization, and summarize the lessons learned and future directions for large-scale digitization at YUL.