Before 1858 wills and administrations were processed in the Prerogative Court and the Consistorial or Diocesan Courts of the Church of Ireland. From 1858 onwards grants of probate and administration were made in the Principal Registry and District Probate Registries, which were adjuncts of the civil court system. For convenience, the two systems of processing wills, church pre-1858 and civil post-1858, are considered together here.

Nearly all original Prerogative Wills and Administrations were destroyed in 1922, but the indexes have survived, and there is a considerable quantity of copies and abstracts, mostly notably the Betham Abstracts of pre-1800 wills. Again, original Diocesan Wills and Administrations were lost in 1922, and while the indexes have survived, fewer copies and abstracts of this class of record are to be found. The Index to Prerogative Wills 1536-1810 and the indexes to most Diocesan Wills have been printed and are widely available. The position with regard to post-1858 Wills and Administrations is more positive, as transcripts had been kept in the District Registries, and the surviving Grant Books are now divided between the National Archives and Public Record Office of Northern Ireland. In addition, printed Calendars of Wills and Administrations were produced from 1858 onwards containing brief details concerning the deceased and executors, and these are on the open shelves with a master index for the years 1858-77.

Various copies and abstracts of all classes of wills have been and continue to be acquired by the National Archives, and these are covered by a Testamentary Card Index (note that this index does not include entries in the Betham Abstracts and District Registry Grant Books). Other important accessions include Inland Revenue Registers containing abstracts of wills and administrations 1828-39, and Charitable Donations and Bequests Books abstracting wills which mention charitable bequests from 1800 onwards. It should also be noted that copies and abstracts of wills are held in other repositories, particularly the Public Record Office of Northern Ireland, the National Library of Ireland, the Genealogical Office (indexed in Analecta Hibernica, 17), the Registry of Deeds (abstracted in three volumes published by the Irish Manuscripts Commission) and the Representative Church Body Library.