Pope Gregory X stood at the very centre of the crusading movement in the later thirteenth century. An able diplomat, he showed himself adept at navigating the political waters of Europe and the Mediterranean World. His crusade gained the participation of virtually all of the leaders of Western Europe, and even the Byzantine emperor and the Ilkhan of the Mongols: crucial if his crusade were to have a chance of defeating the very formidable and successful Mamluk Sultan Baybars. However, Gregory's premature death put paid to his crusade plans. Perhaps because of this, Gregory has hitherto been somewhat neglected by historians - a gap which this book aims to fill. It provides a full account of his contribution to the Crusade, demonstrating that he left a lasting mark on how crusading would operate in the years to come. Philip Baldwin received his doctorate from Queen Mary, University of London.