The Revision Books are also known as the Cancelled Land Books, and essentially continue the work of Griffith's Valuation, which was carried out in the Northern counties as follows:
- Antrim in 1861/2
- Armagh in 1864
- Derry in 1858/9
- Down in 1863/4
- Fermanagh in 1862
- Tyrone in 1851
The books can also be helpful if you're looking to trace living descendants of the householders listed in Griffith's Valuation.
Due to their nature, Revision Books are searchable by location rather than name, and they have been digitised and indexed for online release in the same manner. So get those townland names, with details of poor law union, parish, barony etc primed!
I'm sure this release is going to be a hugely popular addition to the online genealogy armoury of Northern Ireland. And the records will, of course, be free to search and view.
UPDATE: Revision books are live, here.