The aristocracies of medieval Europe used many means to protect and improve their positions. In their choices of spouses, in the arrangements that they made for their children's inheritance, and in their relations with their lords, cousins, neighbours and followers, the great landowners made far-reaching decisions to ensure the prosperity of their lineages. How far did the presence of the border of Normandy affect the strategies of local magnates ? Their activities and attitudes represent one of the best guides we have to the significance of the political divide between Normandy and its neighbours. When a frontier lord arranged a marriage for his son or daughter, was his choice of spouse determined by the proximity of the Norman border ? Was it expedient for frontier lords to divide their French from their Norman lands, in disregard of conventional inheritance practices ? How far would a magnate who owed allegiance to the duke of Normandy associate himself in legal actions, whether by standing surety or witnessing ceremonies of endowment, with those of his neighbours and kinsmen who owed no such allegiance ? A number of these concerns will be studied here to show how they illuminate aristocratic mentalities along the Norman frontier in the twelfth and early thirteenth centuries. Whereas the functions of marriage in medieval noble strategies are familiar to historians of medieval Europe, the manipulation of ties of kinship and neighbourhood, notably for suretyship, has been far more neglected; it none the less reveals much about the associations between the Normans and their neighbours.