Starting in the late 1700s, many Hebrew and Jewish books included lists of people who subscribed to the book before it was printed, thus helping to fund the book’s publication. These lists, which have not been studied comprehensively, are a gold mine of information not only for information about hundreds of thousands of individual Jews, but also on reading habits, names, the growth of communities, travel routes, local institutions, and a wealth of other information. This talk will describe the hamapah.org Prenumeranten Project and present some of our initial findings.