Thom's Official Directory of Ireland

A recent addition to Ancestry is Thom's Official Directory of Ireland for 1904. It's a substantive book - more than 2,200 pages. Ancestry describes it as including:

A Dublin street directory; names, addresses, and occupations for residents of other towns and districts in the country as well; and a wide variety of happenings, institutions, businesses, and departments for Ireland and the UK, including the following:

• county fairs and markets in Ireland
• Parliamentary directory
• civil service and law directory for Great Britain
• navy, army, and militia directory
• colonial directory
• universities, colleges, schools
• churches and ecclesiastical directory
• county and borough directories
• postal directory
• peerage

There is a detailed table of contents, which can help, but Ancestry didn't apparently judge the quality of the typeface adequate to meet their OCR standards. You browse it as you would a book.

Thom's Irish Almanac and Official Directory, the original title, was first published in 1844. The company is still in the directory business, www.thoms.ie

There are various sources for older editions.

Google Books has the 1857 edition with 1,116 pages, indexed and free here.

A Dublin Street Directory from Thom's Irish Almanac and Official Directory for the Year 1862, free here.
FindMyPast has indexed versions of the 1884 and 1910 editions at its various commercial sites, including here.
Eneclann and Archive CD Books have various editions between 1868 and 1910, available for purchase through Archives CD Books Canada
The editions for 1894 and 1914 are available from World Vital Records, pay, here.

A few transcriptions for parts of Ireland for some years can be found through your favourite search engine.

You may also be fortunate enough to be close to a library with original volumes.