From ancient times Irish society was organised around traditional kinship groups or septs/clans. These clans traced their origins to larger pre-surname population groupings or clans such as Uí Briúin in Connacht,Dál gCais in Munster, Uí Neill in Ulster , and Fir Domnann in Leinster. Within these larger groupings there tended to be one clan who through war and politics became more powerful than others for a period of time and the leaders of some were accorded the status of royalty in Gaelic Ireland.  Some of the more important clans to achieve this power were Ó Conor in Connacht, Ó Brien of Thomond in Munster, Ó Neill of Clandeboy in Ulster and Kavanagh in Leinster. The largely symbolic role of High King of Ireland tended to rotate among the leaders of these royal clans. The larger or more important clans were led by a Taoiseach or Chief while the smaller and more dependent clans were led by Chieftains. Under Brehon Law the leaders of Irish clans were appointed by their kinsmen as custodians of the clan and were responsible for maintaining and protecting the clan and its property. This clan system formed the basis of society in Ireland up to the 17^th century.

Often, clans are thought of as based on blood kinship alone; in fact Irish clans would be better thought of as akin to the modern-day corporation (Nicholls, 2003). Their ruling structure, whether ruled by a single lord or a council, changed according to needs and the qualities of their membership. As with a modern corporation, the power of clans grew and shrank. Once-powerful clans could in time decline in stature and be amalgamated into once-smaller ones. How this "merger" would be dealt with would be a matter of negotiation based on the respective power of each party. Consequently, Irish clans were composed of those who were related by blood but also by those who were adopted and fostered into the clan as well as those who joined the clan for strategic reasons such as safety or combining of lands and resources. However, all members of the clan bore the same surname.

The early 17^th century was a watershed in Ireland. It marked the destruction of Ireland's ancient Gaelic aristocracy following the Tudor re-conquest and cleared the way for the Plantation of Ulster.  In 1607 the senior Gaelic Chiefs of Ulster (Ó Neill, Ó Donnell and Maguire) left Ireland to recruit support in Spain but they never reached their intended destination and instead eventually arrived in Rome where they remained for the rest of their lives. After this “Flight of the Earls”, the English authorities in Dublin established real control over all of Ireland for the first time. They brought a centralised government to the entire island and successfully disarmed the native clans and their Chiefs.

However, despite the loss of their traditional lands and forced emigration into the service of Catholic monarchs across Europe, the spirit of the Irish clans remains. To this day Irish people in Ireland and around the world can tell you the name of the clan to which their people belong. The growing influence of the Gaelic League at the turn of the twentieth century rekindled an interest in Gaelic culture and prompted a cultural revival. In the 1940s Chief Herald of Ireland, Edward MacLysaght , drew up a list of Irish clans and the first modern Irish clans were re-formed in the latter half of the twentieth century. Today, these clans are organised in Ireland and in every continent around the world.

In 1991, sixteen of the nineteen known bloodline Chiefs were received at Áras an Uachtaráin by the President of Ireland, Dr. Mary Robinson. This was the first time in modern history that the bloodline chieftains ofIreland had gathered in one place to form a new Council of Irish Chiefs. In 2007, all Irish Clans were invited to send a representative to Rathmullen in Co. Donegal to participate in the Commemoration of the 400^thanniversary of the Flight of the Earls. The only other meeting of this kind ever to have taken place was before the Battle of Kinsale in 1603.