This is the first comprehensive study of an ingenious number-notation from the Middle Ages that was devised by monks and mainly used in monasteries. A simple notation for representing any number up to 99 by a single cipher, somehow related to an ancient Greek shorthand, first appeared in early-13th-century England, brought from Athens by an English monk. A second, more useful version, due to Cistercian monks, is first attested in the late 13th century in what is today the border country between Belgium and France: with this any number up to 9999 can be represented by a single cipher. The ciphers were used in scriptoria - for the foliation of manuscripts, for writing year-numbers, preparing indexes and concordances, numbering sermons and the like, and outside the scriptoria - for marking the scales on an astronomical instrument, writing year-numbers in astronomical tables, and for incising volumes on wine-barrels. Related notations were used in medieval and Renaissance shorthands and coded scripts. This richly-illustrated book surveys the medieval manuscripts and Renaissance books in which the ciphers occur, and takes a close look at an intriguing astrolabe from 14th-century Picardy marked with ciphers. With Indices. "Mit Kings luzider Beschreibung und Bewertung der einzelnen Funde und ihrer Beziehungen wird zugleich die Forschungsgeschichte - die bis dato durch Widerspruechlichkeit und Diskontinuitat gepragt ist - umfassend aufgearbeitet." Zeitschrift fuer Germanistik.