Brian Boru in the context of "Macroom"

The history of Ireland 795–1169 covers the period in the history of Ireland from the first Viking raid to the Norman invasion. The first two centuries of this period are characterised by Viking raids and the subsequent Norse settlements along the coast. Viking ports were established at Dublin, Wexford, Waterford, Cork and Limerick, which became the first large towns in Ireland.

Ireland consisted of many semi-independent territories (túatha), and attempts were made by various factions to gain political control over the whole of the island. For the first two centuries of this period, this was mainly a rivalry between putative High Kings of Ireland from the northern and southern branches of the Uí Néill. The one who came closest to being de facto king over the whole of Ireland, however, was Brian Boru, the first high king in this period not belonging to the Uí Néill.

The Battle of Clontarf (Irish: Cath Chluain Tarbh) took place on 23 April 1014 at Clontarf, near Dublin, on the east coast of Ireland. It pitted an army led by Brian Boru, High King of Ireland, against a Norse-Irish alliance comprising the forces of Sigtrygg Silkbeard, King of Dublin; Máel Mórda mac Murchada, King of Leinster; and a Viking army from abroad led by Sigurd of Orkney and Brodir of Mann. It lasted from sunrise to sunset, and ended in a rout of the Viking and Leinster armies.

It is estimated that between 7,000 and 10,000 men were killed in the battle, including most of the leaders. Although Brian's forces were victorious, Brian himself was killed, as were his son Murchad and his grandson Toirdelbach. Leinster king Máel Mórda and Viking leaders Sigurd and Brodir were also slain. After the battle, the power of the Vikings and the Kingdom of Dublin was largely broken.

The Cycles of the Kings or Kings' Cycles, sometimes called the Historical Cycle, are a body of Old and Middle Irish literature. They comprise legends about historical and semi-historical kings of Ireland (such as Buile Shuibhne, "The Madness of King Suibhne"), stories about the origins of dynasties and peoples (such as The Expulsion of the Déisi), accounts of significant battles (such as Battle of Mag Mucrama), as well as anecdotes that explain rites and customs. It is one of the four main groupings of early Irish sagas, along with the Mythological Cycle, the Ulster Cycle and the Fianna Cycle.

The kings that are included range from the almost entirely fictional Labraid Loingsech, who allegedly became High King in the 4th century BC, to the entirely historical Brian Boru. Other kings include Cormac mac Airt, Niall of the Nine Hostages, Conall Corc, Diarmait mac Cerbaill, Lugaid mac Con, Conn of the Hundred Battles, Lóegaire mac Néill and Crimthann mac Fidaig. It was part of the duty of the medieval Irish bards, or court poets, to record the history of the family and the genealogy of the king they served. This they did in poems that blended the mythological and the historical to a greater or lesser degree.

Medieval Irish historical tradition held that Ireland had a High King (Ard Rí) based at Tara since ancient times, and compilations like the 11th-century Lebor Gabála Érenn, followed by Early Modern works like the Annals of the Four Masters and Foras Feasa ar Éirinn, purported to trace the line of High Kings. John T. Koch explains: "Although the kingship of Tara was a special kingship whose occupants had aspirations towards supremacy among the kings of Ireland, in political terms it is unlikely that any king had sufficient authority to dominate the whole island before the 9th century". Máel Sechnaill I is often considered the first historical High King, although he faced some opposition. Applying the title to earlier kings is considered anachronistic, while kings from before the 5th century are generally considered legendary. The traditional list of High Kings is thus a mixture of historical facts and legend.

The annals describe some later High Kings as rígh Érenn co fressabra ("Kings of Ireland with opposition"), which is a reference to the instability of the kingship of Tara from the death of Máel Sechnaill mac Domnaill in 1022. He had been overthrown by Brian Boru in 1002, and restored in 1014 following Brian's death, but Brian's example was followed by many other dynasties in the century following 1022. The High Kingship was effectively ended in the 1170s after the Anglo-Norman invasion, its last holder being Ruaidrí Ua Conchobair.