In addition to Roman Catholic parish registers, records of landed estates, newspapers and directories, the NLI holds a wealth of information that can be used to trace the history of a family. This includes published family histories, photographs, and manuscript letters and diaries. Local history society publications often contain useful information on local sources such as gravestone inscriptions.
You can search for these items in the Catalogue and Sources database.
Information on dating your family photographs is available in the presentation Dating Irish Family Photographs Dating Irish Family Photographs.pdf (1.51 MB, Adobe PDF) by photo historian and blogger Orla Fitzpatrick.
The NLI also provides free on-site access to a number of subscription websites which are helpful for genealogical research. These include:
Irish Newspaper Archives
Irish Times Digital Archive
19th Century British Library Newspapers
Dictionary of Irish Biography
Oxford Dictionary of National Biography
The Times Digital Archive
House of Commons Parliamentary Papers