Kinship without a doubt played a very important role in Celtic societies in late prehistory. The importance that ancestry had for the late prehistoric Celts is stressed by several classical authors, and seems – at least for some areas, in some periods – also be confirmed in the archaeology by the effort put into burials. The structure of Celtic kin-groups can be reconstructed to some extent, but little of internal kinship relations will have been formalised in a way that could be considered law. There are, however, a number of important legal principles that can be reconstructed, which are related to kinship or external kin-group relations. There is relatively strong evidence for a customary requirement for kin members to support and help each other, in everyday life as much as in legal disputes. This seems to be evident from historical sources, and would fit well with what we find in the early medieval Irish and Welsh laws.