The Second Vatican Council (1962-65), also referred to as Vatican II, was the most momentous event in the life of the Roman Catholic Church during the twentieth century and it brought to a close what some commentators have described as 'the long nineteenth century', a timeline stretching from the period of the French revolution to the 1960s. The council was a call to renewal, or 'aggiornamento', whereby the church returned to its sources in order to strengthen and deepen its capacity to engage with modern society. This thesis assesses the degree to which Vatican II was received in the Roman Catholic Church in Ireland under the headings of collegiality and 'communio', the modernisation of Irish society, ecumenism and liturgy. In advance of that, it will examine the historiography of church councils together with various understandings of reception. While the reception of a church council is an ongoing process, the thesis is primarily concentrated on the period from the announcement of Vatican II by Pope John XXIII in January 1959 to the death of Cardinal William Conway in April 1977. The reception of Vatican II in Ireland was, on the one hand, aided by a model of church more accustomed to loyally receiving change by directives from above. On the other hand, it was hampered by a lack of theological and intellectual preparedness among clergy and laity. This affected the capacity of the Roman Catholic Church in Ireland fully to realise the renewal which the council sought to achieve. Ireland's deep-rooted identification with an institutional-based traditional and devotional form of Catholicism, the divided nature of the communities in Northern Ireland, the homogenous nature of Irish society in the Republic of Ireland, and the beginnings economic and social change within that society, all impacted upon the capacity of the Roman Catholic Church in Ireland to receive fully the council from the beginning.