At the Monastery of St. Catherine at Mount Sinai is preserved the one Byzantine monastic library that antedates those on Mount Athos, and the only one that retains something like its medieval profile. Kurt Weitzmann and George Galavaris present a catalogue of the sixty-nine illuminated manuscripts from the period between the ninth century and about 1200. The visual documentation amounts to over 700 illustrations, including ornamental decorations, many never before published. The discussions of the manuscripts include palaeographical and codicological data, and information on the history and condition, bindings, illustrations, and iconography and style of each item. A bibliography is also included for each. The introduction gives a survey of the history and vicissitudes of the library, which is now housed in a fireproof building. Some of the manuscripts were certainly produced on Sinai, while others may be attributed to the eastern or western provinces of the Empire. The finest are Constantinopolitan works of outstanding quality and merit. A second volume, to appear later, will include the manuscripts written between the thirteenth and fifteenth centuries.