The identification of a book as having been part of Durham Priory Library is based upon one or more of several criteria. Most of these are based upon those stated by Neil Ker in the second edition of his survey Medieval libraries of Great Britain A list of surviving books (London: Royal Historical Society, 1964) (a supplement was published in 1987 which completely revises the books from Durham, and the information is now held on a developing website. The types of evidence are as follows:

• Binding
• Contents
• Ex libris or donation inscriptions
• Title or pressmark inscription
• Inscription by a monk of Durham Priory
• Liturgical evidence
• Characteristic marginalia
• Recognisable script or illumination
• Recorded in medieval catalogues

These are very generic categories that were designed to cope in the broadest terms with all medieval books, so when used more narrowly to focus on one library the distinction between them can blur and it becomes less easy or necessary to say which of the criteria are being applied. Ker’s approach also does not provide for (or include) certain types of books which were clearly part of the book collection at Durham but which are now categorised as archives.