The work summed up in this thesis is based on detailed "codicological" descriptions and collations of sample passages for about 150 out of the total of c. 230 manuscripts of the Commentary. An attempt has been made to apply the skills of the palaeographer and historian of medieval libraries equally with those of the textual critic in extracting palaeographical and textual evidence from a manuscript treated as a whole. The aim of the work is to discover what the manuscripts themselves can contribute towards the history of Macrobius' text in the Middle Ages, and to distinguish families of manuscripts as a preliminary to the establishing of the text.