This book investigates the origins and lineage of the Irish nation by tracing its ancient pedigrees. John O'Hart, a noted genealogist, compiles extensive genealogical records and historical accounts to reconstruct the family trees and historical connections of prominent Irish families. The work presents a detailed framework for understanding the settlement and development of the Irish people through their ancestral lines.

This work is recognized as a foundational text in Irish genealogy and history, offering a deep dive into the ancestral roots of the Irish people. Scholars and enthusiasts alike consult O'Hart's meticulous compilation for its detailed lineage tracing and historical context. The book's enduring value lies in its comprehensive approach to understanding Irish identity through the lens of its ancient pedigrees.