This is a wonderful intro/review about all things HathiTrust.
From the Abstract:
Research libraries have a mission to build collections that will meet the research needs of their user communities over time, to curate these collections to ensure perpetual access, and to facilitate intellectual and physical access to these collections as effectively as possible. Recent mass digitization projects as well as financial pressures and limited space to store print collections have created a new environment and new challenges for large research libraries. This paper will describe one approach to these challenges: HathiTrust, a shared digital repository owned and operated by a partnership of more than forty major libraries.
The article appears in LRTS (Library Resources & Technical Services) Vol. 55. No. 2