The manuscript must be illuminated. Illuminated is defined as any manuscript that is illustrated or sufficiently decorated. Any illustration at all will qualify a manuscript, however manuscripts that are decorated solely through pen-work initials do not qualify. Marginal doodles, especially those added after the production of the manuscript, will not usually make an otherwise undecorated or unillustrated manuscript illuminated.
The manuscript must be "notable". To be considered notable, a manuscript must be included in at least one of the following: a general survey of illuminated manuscripts, or a survey of manuscripts from specific era and/or region (e.g Celtic nanuscripts, Italian Renaissance manuscripts), or survey of manuscript of a particular type (e.g. Books of Hours) or survey of manuscripts held by a particular institution or set of institutions (note, this does not include exhaustive catalogs), or be a single manuscript with at least one monograph dedicated to it, or which has had a print facsimile published of it (digital only facsimiles published on the internet, do not count.)
Bologna, Guilia (1995). Illuminated Manuscripts: The Book Before Gutenberg. New York: Crescent Books.
Thomas, Walther (1979). The Golden Age: Manuscript Painting at the Time of Jean, Duke of Berry. New York: George Braziller. ISBN0-8076-0923-4.
Walther, Ingo F.; Norbert Wolf (2001). Codices Illustres: The World's Most Famous Illuminated Manuscripts, 400 to 1600. Köln: Taschen. ISBN3-8228-5852-8.