Gaelic Ireland refers to the period when a Gaelic political and social order existed in Ireland, and to the culture associated with it. It emerged in the prehistoric era and lasted until the early 17th century. For most of this period, Ireland was a 'patchwork' hierarchy of territories ruled by a hierarchy of kings or chiefs, who were elected by a system known as tanistry. Warfare between these territories was common. Occasionally, a powerful ruler was acknowledged as High King of Ireland. Society was separated into kin groups and, like the rest of Europe, was structured hierarchically according to class. Throughout this period, the economy was mainly pastoral and money generally not used. A Gaelic Irish style of dress, music, dance, sport, architecture and art can be identified, with Celtic art later merging with Anglo-Saxon styles from Great Britain developing Insular art.
Gaelic Ireland was initially polytheistic/pagan and was mainly an oral culture, although inscription in the ogham alphabet began in the protohistoric period, perhaps as early as the 1st century BCE. The conversion to Christianity accompanied the introduction of literature, and much of Ireland's rich pre-Christian mythology and sophisticated law code were preserved, albeit slightly Christianized. Ireland was an important centre of learning and preserved knowledge during the Early Middle Ages. During this time, Irish monks helped to (re-)spread Christianity along with elements of Gaelic art and culture to Anglo-Saxon Britain and on to non-Christian areas of mainland Europe in the Hiberno-Scottish mission.
In the 9th century, the Vikings began raiding and founding settlements along Ireland's coasts and waterways. These became Ireland's first large towns. Over time, these settlers were assimilated into Gaelic society and became the Norse-Gaels. After the Norman invasion of 1169–71, large swaths of Ireland came under the control of Norman lords. The King of England claimed sovereignty over this territory – the Lordship of Ireland – and over the island as a whole. However, the Gaelic system continued in areas outside Anglo-Norman control. The territory under English control gradually shrank to an area known as the Pale and, outside this, many Anglo-Norman lords adopted Gaelic culture. There was regular conflict between the Irish and the Norman settlers.
In 1542, Henry VIII declared the Lordship a Kingdom and himself King of Ireland. The English then began to conquer (or re-conquer) the island. By 1607, Ireland was fully under English control, bringing the old Gaelic political and social order to an end.