The book investigates the traces left in Schiller's biography, works and thinking by Adam Weishaupt's order of the Illuminati. There was a branch of it established near Schiller's Stuttgart domicile and important luminaries of the order approached him in the Palatinate and in Weimar. The consequences of this for Schiller's work on the Don Carlos theme and in the figure of Marquis Posa in particular are described here for the first time. Later Schiller was to encounter another fervent 'illuminatus', Prince of Augustenberg, a meeting that had repercussions on his ideas about "Aesthetic Education" that have been hitherto overlooked.