This exemplary biography, to a large degree based upon previously unknown or ignored primary sources, offers a close reading of the texts against the broader context. Isabelle embodied both royal sanctity and religious innovation. Analysing her childhood and youth, Sean Field traces the way in which Isabelle resisted the plans of her formidable mother, Blanche of Castile, for her marriage, and carved out recognition for her chosen way of life at the court and more widely. Field highlights the paradox that although her religious formation was directed by Blanche herself, who taught her to fear the last judgement (they even shared some of the same devotional readings), in Isabelle's interpretation the right way of life that followed from such spirituality was not the role of pious Christian wife and mother, but that of a devout virgin. Yet Isabelle did not choose to withdraw from the world into a monastery; rather, she remained a laywoman all her life. After a period of time at court where her reputation for a holy way of life gradually grew to reach the ears of the pope himself, she founded a royal abbey for Franciscan women, Longchamp. She moved to the grounds of the abbey, living in separate quarters and acting as the abbey's patron, and increasingly as a living saint. She put humility rather than absolute poverty at the centre of her Franciscan-inspired ideals. Field demonstrates, however, that far from being a paragon of humility, Isabelle had the power as well as the daring to negotiate a form of life for the community that she founded that corresponded to her wishes. In the context of the friars' increasing unwillingness to take on the care of souls for the female communities, Isabelle's achievement was even more significant. She contributed to the composition of a new rule, and then to its revision to match her vision more exactly: the rule guaranteed the institutional ties of the Sorores minores to the Franciscan order. The rule's influence spread: some sisters refused to accept Urban iv's rule for the Order of St Clare, wishing instead to follow Isabelle's; and aristocratic founders chose it for their new Franciscan houses. Field shows how not only her reputation for holiness, but also the political situation in which both the papacy and the Franciscans were anxious for Capetian support gave Isabelle leverage. The author offers an equally compelling analysis of the construction of Isabelle's sanctity. Isabelle was widely regarded as a saint after her death, by the community at Longchamp, by Franciscans and by the court. Her cult paralleled that of her brother St Louis as proof of Capetian sanctity until the mid fourteenth-century loss of political interest in it. One may disagree with some of Field's arguments, for example I think he underplays the influence of Clare of Assisi's rule on Isabelle's. Yet this in no way diminishes the merit of his book, which combines an admirable attention to detail with an excellent analysis of the political and religious context.