[1] Previously known as Leabhar Uí Dubhagáin, after Seán Mór Ó Dubhagáin (died 1372) of the prominent family of historians and musicians in East Galway, it was later also known as the Book of the O'Kelly's, written at the behest of Muircertach Ó Ceallaigh (d. 1407), Bishop of Clonfert (1378–93) and then Archbishop of Tuam (1393–1407).
The largest single section is devoted to the origins and genealogies of the Ó Ceallaigh dynasty of Uí Maine, its contents updated to the time of compilation.
Works found in this work are quatrains paying tribute to the long reign and continuing prosperity of the Uí Dhiarmada (i.e., the descendants of Diarmuid Mac an Bháird), praising the Mac an Bhairds in their capacity as Chiefs of Cinél Rechta Soghain of east-central County Galway.
MacFhirbhisgh's transcriptions are noted by Nollaig Ó Muraíle as being very faithful compared to surviving portions.
A catalogue was made of the manuscript's contents in the seventeenth century, while it was in the possession of Sir James Ware and before the subsequent loss of certain folios.