From the 5th century onward, native Celtic society existed alongside Irish Christianity, presenting a model for the coexistence of paganism and Christianity, the establishment of written as well as oral traditions, and the development of literacy in both English and Irish. Christianity in Ireland dates to the arrival of Saint Patrick in AD 432.

Monasteries, where members of religious communities lived, served as centers for learning and the arts at a time when the general population could neither read nor write. Irish monasteries produced illuminated manuscripts, elaborately carved crosses, and fine metalwork. The earliest Christian writings survive in a few manuscripts from the 7th through the 10th centuries.

Monks copying manuscripts sometimes wrote short poems in the margins. One such poem, titled by modern scholars as "The Viking Terror," was found in the margins of a 9th-century Christian manuscript. It describes a stormy night bringing the writer relief from worry because the stormy sea prevents Viking raiders from landing on shore. A 9th-century poem entitled "Pangur Ban" likens a cat chasing mice to the monk chasing words.

Many of these personal poems seem modern as a result of vivid imagery: the season's changing light, the cry of a bird, the winter chill. Ireland made no unified response to the Viking raids until Brian Bórú led Irish forces at the Battle of Clontarf in 1014. Bórú's forces routed the Vikings, but he was killed and various small kingships ruled Ireland until the island fell under the control of Normans from England. The Normans began to arrive in 1169.