The beginning of a survey about the trade and economy of the Irish Sea province should note that there has been much general acknowledgement of its importance, but little specific study of it. The wealth and economic vitality of the Irish Sea are frequently mentioned in discussions of insular history during the high Middle Ages, but there has been little scholarly study of its commercial history as a whole. This neglect is not unexpected, especially since the materials customary for economic history begin to appear only late and sparsely in the period. Irish Sea commerce, moreover, is intertwined with other considerations such as the spread of saintly cults – the veneration of St Wulfstan of Worcester at Dublin was due as much to maritime contacts with southeast England as to his patronage of clergy from the town – or the composition of literature; the Irish locations found in the tales of the Mabinogion suggest the avenues of Hiberno-Welsh trade. The following discussion does not propose to remedy the defect, for a comprehensive study would be a book in itself. Merely a few comments will be made concerning some interesting aspects of trade and economy in the Irish Sea province from the tenth to thirteenth centuries, a period of change throughout Europe.