Istria and the Kvarner archipelago are strategically located on the main maritime trade routes connecting the eastern Mediterranean with the western provinces of the Byzantine Empire in the late antique period, and with Carolingian Europe in the ninth century. Ecclesiastical and monastic institutions played a significant role in the establishment and maintenance of these North Adriatic trade networks, and the archaeological material from these sites is essential for understanding the dynamics of exchange within the medieval Byzantine Empire and beyond. The present contribution discusses the vitreous material recovered from several ecclesiastical and monastic sites in the Kvarner Archipelago dating to the 5th to 11th centuries CE. 65 glass fragments were analysed by LA-ICP-MS to determine the major, minor and trace element compositions of the glass raw material. Particular attention is given to window glass and lighting devices in context of a comparative multi-site approach to elucidate the chronological and geographical developments in the supply of glass to this region. The data were compared with glass finds from Italy and the Balkans to determine commonalities and/or local specificities.