Scientific reserach implies progress. Sometimes, however, progress merely consists of a step back to the past, as in the case of the dating of the Prochiron, one of the Byzantine law books dealt with in this study. Recently, progress seemed to imply that the Prochiron had been issued by Leo the Wise in the year 907. This book sets out to show that the Prochiron was promulgated by Basil the Macedonian in the years 870-879, thus confirming the view of Karl Eduard Zachariä von Lingenthal, one of the first scholars who paved a way in the ‘ungodly jumble’ of Byzantine law books. Of course, the present study does not exclusively deal with the dating of law books: their status appeared to be inextricably bound up with their dating. Moreover, recent research has come up with results that shed new light on the Basilica and the Novels of Leo the Wise. Reason enough to investigate Leo’s legislative intentions….. To date and not to date, that is the issue in the realm of Byzantine legal history.