A number of law codes have in the past been in use in the various Celtic nations since the Middle Ages. While these vary considerably in details, there are certain points of similarity.
The Brehon Laws governed everyday life and politics in Ireland until the Norman invasion of 1171 (the word "Brehon" is an Anglicisation of breitheamh (earlier brithem), the Irish word for a judge). The laws were written in the Old Irish period (ca. 600–900 AD) and probably reflect the traditional laws of pre-Christian Ireland.
The codification of Welsh law has been traditionally ascribed to Hywel Dda, king of most of Wales between 942 and his death in 950. This was partly an adaptation of previously existing laws however. Welsh law remained in force in Wales until the death of Llywelyn ap Gruffudd in 1282 for criminal cases, and until the Acts of Union in the mid-sixteenth century for civil cases.
Common features of these codes include an emphasis on the payment of compensation for a crime to the victim or the victim's kin rather than on punishment by the ruler. In other words, all law was tort law, with no "victimless" crimes or crimes against the State.
While occasional references to "common Celtic law" in academic literature, such as Fergus Kelly's Guide to Early Irish Law, seem to imply that there was one original Celtic law from which the various later Celtic laws, some of which are historically attested (see Brehon law, Cyfraith Hywel), evolved, it is unlikely that anything like 'original Celtic law' (or 'common Celtic law') ever existed as a unified, let alone a codified body of law. Rather, it is currently thought that various central and western European societies in later prehistory, commonly lumped together under the name 'Celts', had individually different customary laws, which evolved out of similar social needs, influenced each other considerably over several centuries or even millennia, and thus ended up reasonably similar to each other.
'Original (or Common) Celtic law' thus can only be reconstructed, and only as a generalisation. Such a generalisation does not reflect actual past legal practice, but can only show which general principles are likely to have been typical for many (but not necessarily all) early Celtic laws.