The collection of the William James Center includes the complete works of William James, secondary literature on James and pragmatism, and works of those contemporaries of James that who were of importance to him. The entire collection of books belonging to this special collection on James can seen in the catalogue of the library of the University of Potsdam http://info.ub.uni-potsdam.de/ by typing the command "EXK William“ in the simple search.
In addition, other works of relevance to James-research (for example works of such contemporaries as John Stuart Mill) can of course be searched for directly in the library catalogue.
The Center also collected papers on William James. Here is a list (PDF, 219 kB) of these papers. If you are interested in these papers, please contact the Center.