Exeter glazing, and particularly the Great East Window, is of major importance. For the first time, this study establishes the correct dating, provenance and authorship of all the Great East Window's figure panels and most of its heraldic glass, and substantially rewrites the general history of the Cathedral's glazing. In the process, important parts of the Exeter glass are identified with the output of a previously unrecognized fifteenth-century studio whose work can be traced in Devon, Somerset, Dorset and Wiltshire.