Researchers should consult the the following text, taken from the website of the National Archives of Ireland
Before a will can take effect, a grant of probate must be made by a court. If someone dies without having made a will, the court can grant letters of administration for the disposal of the estate. Since 1858, grants of probate and administration have been made in the Principal and District Registries of the Probate Court (before 1877) or the High Court (after 1877). They are indexed in the calendars of wills and administrations and one or two volumes per year in addition to a consolidated index for the period 1858–1877, are available to consult in the Reading Room of the National Archives of Ireland, Dublin.
Before 1858, grants of probate and administration were made by the courts of the Church of Ireland (the Prerogative Court and the Diocesan or Consistorial Courts). There are separate indexes of wills and administrations for each court in the Reading Room. Some of the indexes have been published of which the most important are Vicar’s Index to Prerogative Wills, 1536-1810 and the Indexes to Dublin Grant Books and Wills, 1270-1800 (now on cd-rom – Index of Wills & Marriage Licenses for Dublin Diocese up to 1800, Flyleaf Press, nd) and 1800-58.
Researchers should consult the Index of Irish Wills, 1484-1858, Testamentary Records at the National Archives of Ireland cd-rom (Eneclann, 1999) for an indication of holdings of abstracts, indexes and transcripts (including the Crosslé, Jennings and Thrift genealogical abstracts) though not all original records survive.