In a statement, the Provisionals confirmed its armed struggle would end from 4pm today and that all IRA units have been ordered to dump arms.
The organisation also confirmed that it had instructed its representative to complete its disarmament process in a way which would enhance public confidence and to do this as quickly as possible.
Two independent witnesses from the Protestant and Catholic churches had been invited to testify to the weapons decommissioning move.
The IRA was responding to a call from Sinn Fein leader Gerry Adams in April toconsider abandoning armed struggle and pursue its goals exclusively throughpeaceful and democratic means.
The statement said it believed that the republican objectives could now be achieved through means other than armed struggle.
"The outcome of our consultations shows very strong support among IRA volunteers for the Sinn Fein peace strategy.
"There is also widespread concern about the failure of the two governments and the unionists to fully engage in the peace process.
"This has created real difficulties. The overwhelming majority of people in Ireland fully support this process.
"They and friends of Irish unity throughout the world want to see the full implementation of the Good Friday Agreement."
Denis Bradley, vice-chairman of the Northern Ireland Policing Board, said he waslooking for a positive response from the Unionist community.
He said: "This is a statement which would never have been made five, 10 years ago, even last October, and people need to acknowledge that.
"Now that it has been made, the implications are very clear. It is an enormous day in the history of these islands."
In a departure from tradition, the IRA statement came in the form of a DVD whichfeatured ex-prisoner Seana Walsh reading it.
The Provisionals' statement said: "Notwithstanding these difficulties, our decisions have been taken to advance our republican and democratic objectives, including our goal of a united Ireland.
"We believe there is now an alternative way to achieve this and to end British rule in our country.
"It is the responsibility of all (IRA) volunteers to show leadership, determination and courage."
The IRA insisted that its 36-year armed campaign had been entirely legitimate.
It acknowledged many people had suffered in the conflict, including republicans.
The statement said: "There is a compelling imperative on all sides to build a just and lasting peace."
The Provisionals addressed nationalist and republican concerns that thegroundbreaking moves from the IRA would affect the defence of their communitiesfrom attack.
The IRA stressed there was a responsibility on everyone to ensure that there was no re-occurrence of what it called "the pogroms of 1969 and the early 1970s.
"There is also a universal responsibility to tackle sectarianism in all its forms."
Mr Adams was expected to urge at a press conference in Dublin today that everyone involved in the peace process should recognise the historic nature of the IRA's move.
But unionists, particularly the Rev Ian Paisley's Democratic Unionists, will be sceptical about the IRA statement and will demand proof that its words will be matched by deeds.
Former SDLP leader and Nobel peace prize winner John Hume said today's IRAstatement is very important and it is now up to the British and Irishgovernments and the Northern Ireland parties to implement the Good FridayAgreement.
He said all true democrats now had to respond to the will of the people.
"I think it is a very important step, given the opposition that was coming from the DUP in particular," he said.
"Now that the road is totally clear, I would be reasonably confident that we would make further progress.
"It is now the duty of all true democrats north and south to implement the will of the people. That's the strongest argument that can be put to the parties in the North.
"I think it should make quite a substantial difference. Obviously, a complete and absolute end to violence is a necessity in our situation.
"Violence not only has no role to play, but it deepens the problems and makes them far more difficult to resolve. It's about time that that was completely ended," he told Sky News.
Mr Hume called for the British and Irish governments to meet the Northern Ireland parties immediately to set about implementing the Good Friday Agreement.
Democratic Unionist Party MP Jeffrey Donaldson said any possibility of thefuture resumption of power-sharing would depend on how long it takes the IRA tocomplete decommissioning and how it is verified.
The Lagan Valley MP said: "That will be determined by how long it takes the IRA to complete the decommissioning process. We've no indication in this statement of when that will be done, they simply say it will be done as soon as possible.
"We don't know whether that means one week, two weeks, six months, a year, so obviously we need to wait and see what happens there.
"We need to see that what happens is properly verified and when the IRA talk about enhancing public confidence, how do they intend to do that? What will be the role of the independent witnesses and how much will they be able to say about what they've seen and about what has happened?"
Mr Donaldson said more clarification of the statement was needed.
"That's why we'll probably need a period of time now over which we can judge whether what the IRA says is what they actually do," he added.
SDLP leader Marc Durkan said the statement appeared to show the IRA had brokenwith its past, and he hoped the organisation's involvement in organised crimewould end for good, as well as the culture of cover-up and community control.
It was vital, he said, that the Provisionals deliver quickly on what they have promised. Actions on the ground must demonstrate this- and there is an equal obligation on all loyalist paramilitaries to end their terror and crime.
Mr Durkan added: "There is also an onus on the two governments and the unionist parties to work together to deliver the full implementation of the Good Friday Agreement."
He added: "The use of violence was always immoral and unjustified. It achieved absolutely nothing and brought incalculable suffering to victims throughout the north. They, and their loss, should be first and foremost in our minds today."
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