The eastern arm of Merton College chapel contains one of the two most important schemes of stained glass to survive from early fourteenth-century England (the other being found in the nave of York Minster). As such, it forms the centerpiece of Tim Ayers's impressive study of Merton's entire stained glass collection, which extends beyond the chapel to the library, the hall and the warden's lodgings, and in date from the fourteenth century to the nineteenth. One of the many strengths of Ayers's study lies in his ability to present the glass in context. This substantial two-part work forms the latest addition to the Corpus Vitrearum Medii Aevi series, funded by the British Academy, and so the focus is rightly on the medieval material. Ayers demonstrates, however, the extent to which an exploration of Merton's post-medieval history – social, ecclesiastical and architectural, as well as art historical – is necessary for a proper understanding of that medieval inheritance. He carefully disentangles complicated stories of expansion and restoration and shows the glass to be an important constitutive and contributive element in the evolution of the college over more than seven centuries. His extensive archival research enriches the account in many ways, not least by filling out the identities of Master Henry Mansfield and William de Thame, the principal patron and probable painter of the early chapel glass, respectively. Through his exploration of Merton's glass, Ayers also offers new and valuable insights into the development of medieval educational institutions more generally, the wider architectural history of both Merton and Oxford, and the significance of Thame as an important fourteenth-century centre of stained glass production. Much of this historical context is set out in an excellent general introduction and expounded in the first part of each of the four subsequent sections, each of which is then completed by a comprehensive catalogue. In order, these sections cover the glass in the eastern arm of the chapel, the transepts, the hall (now displaced) and the Old Library. A short fifth section considers the small but instructive record of the glazing of Fellows' rooms in Mob Quad, and a sixth the history of the glass in the warden's lodgings together with a catalogue of its (almost entirely post-medieval) remains. Part i is prefaced with bibliographical and reference material and part ii rounded off with four appendices and thirty-two colour plates. This is an impressive work of scholarship that will serve as a standard resource for many years. For a study of a single artistic medium on a single site its relevance is unusually broad. Any desire for a greater number of colour reproductions is mitigated in this case by the excellent archive of images on the Corpus website (www.cvma.ac.uk), alongside which it can easily be used.