Following is a listing of information on the chief families which made up the tribes and clans of Ireland and Scotland in the mid-sixteenth century. These are the families that had tribal significance, holding some direct political power on the primary, inter-tribal or national level, either as main players, or as constituent support groups of a more local (but nonetheless tribal) nature.

The families are arranged within their respective ethnic groups by tribe, sub-tribe and clan. Implicit here is the understanding that each of the five ethnic groups of Gaeldom fostered related tribal populations, and that these tribal populations comprised the basic political and social structure of Ireland and the Scottish Highlands until the seventeenth and eighteenth centuries.

Every Gaelic tribe originated in one or another of the five ancestral ethnotribal population groups of Gaeldom, hence the division of Part II into five chapters. The charts which precede each chapter show the relationship of each tribal branch to one of the five euhemerized Celtic ancestor-deities traditionally linking the tribes of that particular ethno-tribal group. Sub-tribal branches of an independent and geographically isolated nature are branched independently on the chart but are linked in the text. The position of the tribes on the chart is generally indicative of their relative locations within Gaeldom.