This book describes, for the first time, the nature of the unique socio-political and economic system of Gaelic Ireland as it developed and changed during the period from her eariest history until the Anglo-Norman invasion, with special emphasis on the period of the eleventh and twelfth centuries. The origins of this nationwide system are explored in their European context, and the components of the system: local kingdom, trícha cét, late-túath and baile biataig, are explored, described and understood. Special attention is given to the role of kingship in this early society, as well as to the lesser grades within society. Especial attention is paid to the trícha cét, and it is demonstrated that this unit was adopted unchanged by the Anglo-Normans to become their cantred. A large part of the book is taken up with the task of listing and describing the area of each cantred by use of a newly developed methodology which makes use of the fulsome material from the Anglo-Norman period. An additional dimension of this task is that, once established, these borders can then be used to reconstruct in great detail the political borders of pre-Invasion Ireland. A methodology of border and boundary study is established and described, and the close relationship between Gaelic and Anglo-Norman boundaries and borders is investigated and demonstrated. In the course of defining and then applying this methodology, a number of other units are considered, especially the ecclesiastical divisions of parish and rural deanery. Other units merit attention as the forerunners of our modern townland system. These include the Anglo-Norman vill, as well as the sub-divisions of the baile, known by different names in various parts of the country, such as the leathbhaile, quarter, cartron, ballyboe, tate, etc. This is the first book to be published on this neglected and important area of study, which last received significant attention as long ago as 1929 at the hands of Prof. James Hogan.