‘The king will reign and he will deliver judgement and justice on earth.’ This bold prophecy of Jeremiah 23. 5 (et regnabit rex et sapiens erit et faciet iudicium et iustitiam in terra) provides a guiding theme for the De informatione principum [DIP]. The Latin text of this treatise, written to instruct the future Louis X of France (1289–1316; r. 1314–1316), son of Jeanne of Navarre (1273–1305; r. 1285–1305) and Philip IV of France (1268–1314; r. 1285–1314), survives in a dozen manuscripts. DIP attracted brief attention from Léopold Delisle in the nineteenth century, who thought that it might have been composed by a Dominican friar on the evidence of a rubric in a fifteenth-century copy of the translation, but he did not study its arguments in detail. In fact, DIP shares so many themes and passages in common with the Speculum dominarum composed by Durand of Champagne, Franciscan confessor to Jeanne de Navarre, that, as will be argued here, there are good grounds for attributing both works to the same author. The treatise about the education of a prince is not just an exhortation to virtue in the model of earlier ‘Mirrors of Princes’, but an exposition of abuses that its author sees as prevailing in the royal court. This study surveys the tradition of such writing prior to DIP in order to examine how it fits into an ever-evolving tradition, comparing it in particular to that of Vincent of Beauvais on the moral education of a prince.