The social structure of Iron Age Celtic society was highly developed. It was a tribal society that was bonded together by a complex system of laws and social customs. The established body of Law was known as 'Fenechas', the law of the Feine (Freemen), or more commonly, the Brehon Law. This body served the People for centuries.
The most common body of Brehon Law was codified in 438 CE, by the order of Laighaire, a High King of Ireland. The proceedings by which this work was done by Three Kings, Three Brehona (Recitors of the Law), and Three Christian missionaries. By this act Pagan Fili and Christian Monk came together and worked out a set of laws that was workable for people of both religions. The body of that law has been transmitted to us in the volumes known as the Senchus Mor. The body of Law known as Brehon Law, as contained in the Senchus Mor is a body of national law. However, national law was secondary to local law. Whether local or national it was the Brehons who acted as the recitors of the Law. There has been some confusion about who acted as the judge. It was the nobility who acted as such. As stated the Brehons were the recitors of the Law. After the Brehon had recited the Law, only then could the King or Queen render a decision. This is why lore is replete with examples of the Kings or Queens Druid, actually the Ard-Fili, having the right to speak before the King. If the Brehon, who was a member of the intellectual/skilled caste, recited the law incorrectly they were expected to forfeit their fee and pay damage costs. The Brehon laws were responsible for regulating how people interacted. Hospitality, etiquette and other things were set out in ways that left little room for doubt. The codes of behavior established in the Law was such that all members of a family had to adere to it. Codes of behavior and levels of responsibility were laid down in the laws for each social group. The more responsibility a social group had, the more restrictions were placed on them. Status was determined by the ownership of cattle and a few other things. There was no concept of land ownership in early Celtic society. This stands in sharp contrast to the Roman and Anglo patterns.
In the modern Tribe we primarily utilize the Triads as our body of Law. We see the Triads as a contraction containing the very Spirit of the Brehon Law. We are also bringing forward applicable sections of the Law for use today.
In case of contract law this usually was made by declaring the pledge of the other side as forfeit, thereby forcing the other side either to loose their honour or to settle the claims in court.
Generally, Canon Law seems to have preferred death penalty in cases where the honour-price of the offender was lower than the penalty, and it additionally made the realtives of the offender liable for the fine.
Therefore, most elements of old CelticLaw are at best reconstructable from the Irish and Welsh Laws and their similarities, especially where those similarities are on a linguistic basis that shows that the terms for certain legal things were derived from a common Gaulish word.