Liber Flavus Fergusiorum

Liber Flavus Fergusiorum ("Yellow Book of the Ó Fearghuis", aka RIA MS 23 O 48 a-b, is a medieval Irish text, dated to c. 1437-40.
Ó Fearghuis.
Ó Fearghuis was the name of a Gaelic-Irish medical family from Connacht. The surname is now generally rendered as Fergus. The family were originally based at Roscam, in Clann Fhergail (between Oranmore and Galway City). In the 13th century they seem to have removed to north Connacht, to what would later become County Mayo. During the 14th-century members of the family created the manuscript which would come to be known as Liber Flavus Fergusiorum. The last member of the family to own it was John Fergus, who died in Dublin about 1761.
The Liber was composed at various times by several different scribes, the principal one identifying himself as Aedh. Two translators, Seaán Ó Conchubair and Uidhisdín Mag Raighin, are named in colophons. Ó Conchubair translated a work on the Office of the Dead into Irish, while Mag Raighin translated the Life of John the Evangelist.
The book derives its name from the Ó Fearghuis family, whose descendant, Dr. John Fergus, brought the manuscript from County Mayo to Dublin in the 18th century. Upon his death in 1761, it was held by his daughter, Frances Arabella Kennedy, whose grandson deposited it in the Royal Irish Academy in 1875.
The Academy's website describes the book thus:
"manuscript is of Connacht provenance and from the names of places mentioned, written in Co. Roscommon. The contents are mainly religious tracts, lives of the saints, passions and homilies and some legendary episodes from the Ulster cycle and the tale of Fortinbras (Stair Fierabhrais). The writing is in double columns and initial capitals are coloured throughout Vol.1 but not in Vol. 2. The manuscript is in fairly good condition with leather binding; some leaves are badly stained with consequent complete or partial obliteration of the content."