Collections of primary source materials present interesting challenges for researchers. Many collections are still housed in special collections and archives at university libraries and research centers. A growing number of collections have been digitized or are targeted for digitization. Some of these efforts end up online for free to users, though the institution absorbs the cost of online hosting; others end up digitized and hosted by publishers and sold back to libraries. Sponsorship efforts are also underway to make the costs sustainable and open access to the public. Below you'll find a variety of these efforts.