Nearly all major studies of contemporary documentation for medieval art in England fail to take into account the vast body of testamentary evidence. This study brings together for the first time a large corpus of wills relating to windows and their glazing, using a wide range of published and unpublished wills and benefitting from fieldwork undertaken to relate bequests to existing fabric and glazing. Most of the wills relate to parish churches, but there is also much evidence concerning cathedrals and religious houses; the last category is particularly important, as so little glazing has survived from such foundations. Testators span almost the entire social spectrum: monarchs and magnates, prelates and parish priests, gentry, lawyers, merchants, and (especially from the late 15th century) the more prosperous husbandmen and yeomen. The wills of a score or so of glass-painters also feature. Women are represented, not only as testators, but as executors and heiresses. Dates range from the late 13th century to the Reformation. The result is a treasure trove of information concerning patronage, iconography, commemorative strategies, costs, techniques, processes, and dating, which will be of value to historians of art, religion, culture, society at a local level, as well as to architectural scholars.