My research on the political uses of scientific knowledge in Renaissance Hungary began with a manuscript, an astrological prognostication on a comet that appeared in 1468. The manuscript had previously been in the Sárospatak library in eastern Hungary but was now in the state library in Novgorod. The text was dedicated to the Hungarian king Matthias Corvinus, interpreted for him the dire effects that would follow from this comet, and was signed “The Canon of Zagreb.” Here again a monarch employed astrological expertise in matters of state. Further research turned up other texts by this “Canon of Zagreb” and revealed him to be the Polish astrologer Martin Bylica from Olkusz, a town not far from Krakow. From this I pieced together a biography of Martin Bylica and assembled a bibliography of manuscripts in archives from Krakow to Rome.