Wills, which were proved in the Welsh ecclesiastical courts before the introduction of Civil Probate on 11 January 1858, have been deposited in the Library. The old indexes produced by the courts themselves have now been replaced by a new online index.

The covering dates of the surviving probate records are:

• Bangor: 1635 - 1858
• Brecon: 1543 - 1858
• Chester (Welsh wills): 1557 - 1858
• Hawarden: 1554 - 1858
• Llandaf: 1568 - 1857
• St Asaph: 1565 - 1857
• St David's: 1556 - 1858

For the period after 1858 the Library has custody of register copy wills from 5 registries, covering all but one (Montgomeryshire) of the Welsh counties, and a full set of the annual index of all wills and administrations granted in England and Wales, known as the Calendar of Grants, from 1858 to 1972.

In addition to the official probate records, some wills and inventories and other papers associated with probate can be found in the consistory court papers filed with the diocesan records of the Church in Wales. Thousands of wills occur in the Library's collections of family, estate and personal papers; some of these may not survive in the official probate records, or may never have been proved, or may have been proved outside Wales. These can be searched through the online Archives and Manuscripts catalogue.