This chapter reviews the development and after-effects of the Norman Conquest of England in Scotland, Wales and Ireland, which made they felt far into the twelfth century and beyond. As in England, long reigns made for political stability, strengthened by the fact that the five rulers represented only two different generations. Three brothers, Edgar, Alexander I and David I, were followed by David's two older grandsons, Malcolm IV and William I 'the Lion'. The Welsh, united culturally by their use of a P-Celtic version of the common Celtic family of languages, were a pastoral people organized in clans, recognizing the superior chiefship of warring dynasties which would claim the right to provide a king over a distinct gwlad. In Irish history the twelfth century must always be the age of conquest, mostly belonging to families of Norman, Flemish, Breton or other continental background, exploited their military skills and techniques to acquire kingdoms and trading towns in the south of Ireland.