''TheCroinic nó leabhar oiris is ea '''''AnnalsAnnála of Tigernach''Tiarnaigh''' ([[Abbreviation|abbr.]]giorrúchán '''AT'''), is adócha tosaithe i g[[chronicle]]Cluain probablyMhic originating in [[ClonmacnoiseNóis]], i n[[IrelandÉirinn]]. ThelanguageScríobhadh is aiad mixtureas of [[Latin language|LatinLaidin]], andagus [[Old IrishSean-Ghaeilge|OldSean-]] andagus [[MiddleMeán-Ghaeilge Irish]].
''Many of the pre-historic entries come from the 12th-century MS, [[Rawlinson B 502]].<ref name=Hughes>Hughes, ''Early Christian Ireland: Introduction to the Sources'', ppll. 99-162.</ref> However, the real importance of the chronicle is for the period 489-766, 973–1003 and 1018–1178.<ref name=Hughes /> These three fragments survive from the 14th-century MS [[Rawlinson B 488]].<ref name=Hughes /> The coverage of the period 766 to 973 is lost, but is thought to survive in abbreviated form in the ''[[Chronicon Scotorum|Chronicon Scottorum]]'' (abbrgiorr. '''CT''').<ref name=Hughes /> The latter is defective for the period 718 to 804, but as much of its content is derived from the hypothetical ''[[The Chronicle of Ireland|Chronicle of Ireland]]'' (itself partly derived from the ''[[Iona Chronicle]]''), of which the ''[[AnnalsAnnála of UlsterUladh]]'' (abbrgiorr. '''AU''') and ''[[AnnalsAnnála ofInis InisfallenFaithlinn]]'' (abbrgiorr. '''AIAIF''') are also derived, we have some idea of what the entries contained.<ref name=Hughes /> [[Kathleen Hughes (historian)|Kathleen Hughes]] postulates that AU and AT diverged from the ''Chronicle of Ireland'' sometime before the year 913.<ref name=Hughes />
''The chronicle owes its modern name to ''[[Tigernach Ua Braín]]'' (d. 1088), [[abbotabb of Clonmacnoise]], but this does not mean that he was also its author. A note added to the entry for 1088, the year of his death, in Rawlinson B 488 states that the text was written by Tigernach up to that point. If he was not merely the scribe of the original text copied by the 14th-century scribe, it may mean that he was one of the [[annalist]]s responsible for the work.<ref>Charles-Edwards, "Ua Braín, Tigernach (''d''. 1088)"</ref>
