Norman invasion and settlement in Wales added a new and permanent element to the history of Wales. The extent of Norman settlement and influence might vary, but it was never removed, and from the 1060s it affected Welsh society and Welsh politics very profoundly. For different reasons, it has also affected the study of Welsh history. English historical sources are very rich. The records of the central administration, even when they are far from complete, are a major asset. There is a wide range of narrative sources. English and Norman religious houses acquired lands in Wales, and they maintained elaborate archives; although much has been lost, much has survived. As a result, it is possible to get to know the French settlers in Wales in some depth; their interests, their family links, their religious affiliations and benefactions, their impact on the places where they settled and, for later centuries, their business management, can be examined in detail. By contrast, their Welsh contemporaries are less well recorded and seem often to be shadowy figures. It is dangerously easy to see Wales in the eleventh and twelfth centuries through Anglo–Norman eyes, and so to see only a distorted image of Welsh society.

There is another feature which deserves attention. The spread of the Normans and of Norman influence in Europe in the eleventh and twelfth centuries is a major phenomenon. They conquered England; they settled in southern Italy and Sicily, and there they created new political units.