This is a collection of papers by twenty-thee authors, presented at two colloquia, held in 2011 and 2012, devoted to the memory of St Ambrose in Milan from the early Christian to the modern age. It is part of a broader research project on ‘The memory of the Fathers: survival of the patristic heritage in medieval Italy’. Every facet of this memory is examined from archaeological, philological, historical and liturgical standpoints. Boucheron and Gioanni, coordinators of the project, point out that Italy is well suited to this sort of study, especially Rome for Gregory the Great and Milan for Ambrose, where they had been bishops. In these cities their memory has always been maintained in buildings, liturgical rites and texts; it is pinned to the region. The archaeological studies of the basilicas built by Ambrose suggest that he carried out an architectural project for the city as a whole and transformed Milan into a Christian capital, a fact of primary importance in the Middle Ages. After an eclipse during the Three Chapter Controversy (and the Lombard kingdom), the cult and influence of Ambrose revived during the Carolingian renaissance. The ever-changing iconography of the saint, since he was first portrayed in the fifth century, follows the needs of a changing devotion through the centuries: he is represented with or without a beard, according to the current ecclesiastical discipline; or astride a white horse, armed with a scourge in the late Middle Ages, when he was considered more a defender of his city than a bishop with pastoral care. The manuscript tradition of St Ambrose's works in Milan, traced from the fifth century, attests to a stronger diffusion from the eleventh century, when he was also quite often cited in canonical collections. In the twelfth century a careful edition of the patron's opera omnia was prepared in the basilica named after him. At the same time, with Ambrose as the point of reference, archbishops of Milan claimed a role beside the German emperors: Ambrose in support of a claim to power. The memory of the patron saint was increasingly used for political purposes in the commune of Milan, by the Visconti and later by the ‘Ambrosian republic’. As far as religion was concerned, constant reference to Ambrose marked the episcopate of Charles Borromeo, who also has an image of him on his seal. Examples of a more literary and scholarly approach to the commanding figure of the saint are the imitation of Ambrosian hymns by Marc'Antonio Flaminio during the sixteenth century and an historical study of the ‘Ambrosian’ liturgy during the eighteenth.