A seismic retrofitting project required the UCSB Library (University of California, Santa Barbara) to permanently reduce its on-site collections by 120,000 volumes. To accomplish this successfully, a strong collaboration with the faculty was essential. This article describes a planning process in which the library worked with a faculty committee to implement a campus-wide survey of faculty and graduate students regarding their behaviors and preferences in accessing and using the collections. The survey outcomes informed a common understanding of which physical materials should re- main on-site and which could be moved to storage with the least impact on research and teaching.