Some of the 100 old laws to be repealed by the Government in the autumn date back to 1250, the Taoiseach told the Dáil.
The Attorney General's office has identified 500 Acts that pre-date the State but are still in operation, and 100 of these have been earmarked for repeal.
Mr Ahern said the legislation would be introduced in the autumn, "and in one swoop we will get rid of a sizeable number".
Other old but still relevant legislation would be consolidated as new Acts.
There were "dozens of Acts to do with intoxicating liquor, with one being passed practically every five years from the beginning of time. They are still law in one form or another."
He said there were "all kinds of crazy Acts, but they are still there since they have never been consolidated".
An "enormous number" of water services-related Acts had been passed over the centuries. "They have not been changed, but can now be amended by the Water Services Bill 2003."
Mr Ahern said the benefit would be "a far more progressive statute law that does not create problems for many industries, not to mention legal people. They will no longer need to go back all the time to make the most cogent cases."
The laws for repeal include the Regulation of Chimney Sweeps Act 1840 and the Baths and Washhouses (Ireland) Act 1846. "A whole host of legislation is entirely irrelevant to today's needs," said Mr Ahern.
The Fine Gael leader, Mr Enda Kenny, called on the Taoiseach to make a commitment to resource a review of post-1922 legislation that "lies dormant on the Statute book".
Mr Caoimhghín Ó Caoláin (SF, Cavan-Monaghan) asked if the review would involve the repeal of ground rent legislation which was "a legacy of a bygone day that remains irksome and even worse that that for many".
Mr Ahern said "opinion is divided on whether you can repeal ground rents in such a way as to abolish them".
