The social substratum of Enlightenment in the ancien régime was constituted by the various Enlightenment societies. Learned and Patriotic Societies, Freemason Lodges, Reading Societies, and Secret Societies assembled aristocrats and burghers, scholars and merchants, professors and students with a hitherto unprecedented singleness of purpose. As yet there has been a signal absence of prosopographic studies on this extensive society landscape in terms of the structures displayed by this 'Fraternity of Enlighteners'. In his study the author takes the example of central German societies of this kind and embarks on a systematic analysis of those structures. How many such societies were there in the 18th century, where and when did they exist? Who were the members? Did the societies exist in mutual isolation or were they interconnected via multiple memberships and society 'careers'? Are there indications for a fully-fledged network of 'enlightened' societies?