Entries up to the mid-6th Century are retrospective, drawing on earlier annalistic and historical texts, while later entries were contemporary, based on recollection and oral history. T.M. Charles-Edwards has claimed that the main source for its records of the first millennium A.D. is a now lost Armagh continuation of the Chronicle of Ireland.
The Annals used the Irish language, with some entries in Latin. Because the Annals copied its sources verbatim, they are useful not just for historians, but also for linguists studying the evolution of the Irish language.
The Library of Trinity College Dublin possesses the original manuscript; the Bodleian Library in Oxford has a contemporary copy that fills some of the gaps in the original. There are two main modern English translations of the annals – Mac Airt and Mac Niocaill (1983) and MacCarthy (1893).
Several kings are mentioned throughout the Annals of Ulster. The Annals tend to follow the lives of the kings, including important battles, raids, and their ultimate death. Between the years of 847 and 879, three different kings are highlighted. For example: Máel Sechnaill mac Máele Ruanaid, the king of the southern Ui Neill clan from 846–862: