I here present a list of those institutions or individuals which can be shown to have possessed copies of works by John of Wales. The list is by no means full, even where catalogues and inventories of medieval libraries survive. It can be seen that only some of John's known works are represented on this list: they are those whose titles are easily distinguished in even a scanty inventory, and those which remained firmly associated with John's name. Some of his works were misattributed at an early date, or confused with other works of identical title. Others were often copied anonymously. Thus John's De Poenitentia and De Septem Viciis, for example, are hard to spot unless a catalogue contains incipits. Very many medieval catalogues did not. It is therefore reasonable to assume that, even in the libraries listed here, there will often have been more of John's works than we can tabulate. And many more copies must have existed which went unrecorded and are now lost to us.

I have used two main sources in compiling this list: first, surviving catalogues or parts of catalogues from the medieval period; and, secondly, marks of ownership in surviving MSS and early printed editions of John's works.