It is clear from references in the ninth-century wisdom text The Triads of Ireland that the monasteries of Cork, Cloyne, and Slane were centers of legal learning. No precise information has survived regarding the location where individual law texts were written. There is evidence, however, that the main body of law texts— written in the seventh and eighth centuries—came from two main legal traditions, one based in Munster and the other in the northern Midlands and southern Ulster.
The pre-Norman annals contain references to fifteen persons described as iudex or brithem, "judge," of whom all but four are recorded as having held ecclesiastical office. For example, the Annals of Ulster record the death in 802 of Ailill son of Cormac, abbot of Slane, who is described as iudex optimus, "an excellent judge." In 806 the same annals record the death of Connmach, judge of the Ui Briuin of Connacht: he was evidently a layman. The annals of this period provide no clues as to the operation of the law schools. It is clear from the legal manuscripts, however, that the work of interpreting the Old Irish law texts began as early as the ninth century. The earliest practice seems to have been for glosses to be written between the lines of the text, and to consist largely of explanations of words which might be unfamiliar on account of linguistic change or because they belonged to the specialized legal vocabulary. Most law texts were also provided with commentaries, which expand upon the original text. In the earlier legal manuscripts the commentary is generally fitted into the margins of the page, whereas in later manuscripts of the fifteenth and sixteenth centuries the commentary is given a place in the body of the page.
After the Norman invasion of 1169, clerical involvement in Irish law diminished, and the law increasingly became the preserve of laymen from a small number of legal families. From the evidence of the annals and of the surviving legal manuscripts, it is clear that the MacEgan (Mac Aodhagain) family was the most active and influential of these. There are more references to MacEgans than to any other legal family in the annals, and most surviving legal manuscripts have a MacEgan connection. They had schools in Ormond (Co. Tipperary) and at Duniry, Park, and other locations in County Galway. As well as being academic lawyers, the MacEgans were widely involved in legal practice. Between the fourteenth and sixteenth centuries they are known to have acted as lawyers for most of the ruling families of western and central Ireland. Their patrons included old Gaelic families such as Mac Carthy More, O’Connor Roe, and O’Conor Don, as well as Anglo-Norman lords such as Blake, Butler, and Barrett. The most prominent member of the MacEgan family in the surviving documents is Giolla na Naomh Mac Aodhagain, whose death in battle in 1309 is recorded in the Annals of Connacht, where he is described as "chief legal expert of Connacht and a well-versed general master in every other art." Three works are attributed to Giolla na Naomh. The first is "An address to a student of law," a poem of twenty-five stanzas that summarizes the educational needs of a law student. He stresses the importance of legal precedents as a basis for right judgement, and recommends the careful study of law texts and wisdom texts. Another poem attributed to Giolla na Naomh deals with the law relating to distraint (athgabal). The longest surviving text attributed to Giolla na Naomh is a general treatise on Irish law. It is primarily based on the Old Irish law texts and their associated glosses and commentaries. In addition, there is a significant Anglo-Norman element, which illustrates the degree to which Irish law schools had by this period been influenced by English Common Law. Thus the treatise uses terminology of Anglo-Norman origin such as baranta, "guarantor," and finne, "jury."
Other prominent legal families were the MacClancies (Mac Fhlannchadha) of Munster and the O’Dorans (6 Deorain) of Leinster. One of the most important of all the surviving legal manuscripts, now called Egerton 88, was the product of a minor legal family, the O’Davorens (6 Duibhdabhoireann) of County Clare. This manuscript was compiled by Domhnall O’Davoren and his pupils between 1564 and 1569, and contains a variety of legal material, much of it not preserved elsewhere. The abundant marginal comments are also of great interest, as they provide insight into the life and general atmosphere of a sixteenth-century law school.
The Elizabethan wars, culminating in the Flight of the Earls in 1607, brought about the end of the Irish law schools, as the lords who formerly employed the legal families were dispossessed or adopted English law.
