We should start with a quick look at the basics of the law. The basic regional unit was the tuath and this seems to also be the basic legal unit since Irish Law distinguishes between the deorad (outsider) and the aurrad (person of legal standing within the tuath). Basically stated, the outsider has no legal rights within the tuath and can be killed, maimed or treated in any manner without these acts being considered as legal offences IF there is no treaty between the tribe the outsider came from and the one where he is about to be maimed, killed, or treated badly. He would have legal standing only if there was a treaty between the two tribes.

The second basic of Irish law was rank. Simply said, the higher your rank, the more legal standing you'd have. "An offence against a person of higher rank entails a greater penalty than the same offence against that of a person of lower rank. Similarily, the oath of a person of higher rank automatically outweighs that of a person of lower rank." (Kelly, 1998 p. 7)

Another basic element of the legal system was kinship. The kin group referred to most often in the law texts is the derbfine (true kin) which consists of all descendants through the male line from a common great grandfather. This group has considerable legal rights over its individual members. Each kin group has its own kin land (fintiu) and each legally competent male had some responsibility over this land. It could only be sold with the consent of the kin and if a man has sucessfully fulfilled his obligations toward his kin, he can annul contracts of other members of the derbfine if he feels they are detrimental to the kin group.