This is a new critical edition of the legal treatise by John of Ibelin, count of Jaffa and Ascalon (died 1266). John was a leading magnate in the Latin East, and his first-hand experience of the courts meant that he was well-placed to write authoritatively on his subject. His work is in French and describes in detail the procedures of the High Court of the kingdom of Jerusalem, and the law as administered there. The treatise has long been recognized as being of fundamental importance for the legal, institutional and social history of the Latin settlements in the Levant, and this is the first edition to take into account all the surviving medieval manuscripts and the first to be published since 1841.