800–1168

The first recorded Viking raid in Irish history occurred in 795 when Vikings from Norway looted the island. Early Viking raids were generally small in scale and quick. These early raids interrupted the golden age of Christian Irish culture starting the beginning of two hundred years of intermittent warfare, with waves of Viking raiders plundering monasteries and towns throughout Ireland. Most of the early raiders came from the fjords of western Norway.

The Vikings were expert sailors, who travelled in Longships, and by the early 840s, had begun to establish settlements along the Irish coasts and to spend the winter months there. Vikings founded settlements in several places; most famously in Dublin. Written accounts from this time (early to mid 840s) show that the Vikings were moving further inland to attack (often using rivers) and then retreating to their coastal headquarters.

In 852, the Vikings landed in Dublin Bay and established a fortress. After several generations a group of mixed Irish and Norse ethnic background arose (the so-called Gall-Gaels, Gall then being the Irish word for "foreigners").

However, the Vikings never achieved total domination of Ireland, often fighting for and against various Irish kings. The Battle of Clontarf in 1014 marked the beginning of the decline of Viking power in Ireland. However the towns that the Vikings had founded continued to flourish and trade became an important part of the Irish economy.