This first comprehensive study in English devoted to Sienese painting to be published in four decades centers on the fifteenth century, a fascinating but frequently neglected period when Sienese artists confronted the innovations of Renaissance painting in Florence. The painters of Siena, without betraying their heritage of the previous century?which had produced some of the greatest artists of all time, including Duccio, Simone Martini, and Ambrogio and Pietro Lorenzetti?succeeded in adapting their artistic traditions to a new and completely original vision, rejecting many of the norms by which subsequent generations have come to define Renaissance art. These later Sienese artists frequently took a nonrational approach, seeking not to replicate nature, but to explore a more subjective world?one that in some respects is akin to that of twentieth-century art. The result is one of the most singular schools of Italian painting, which must be viewed on its own terms and understood within the religious and social framework of fifteenth-century Siena.