Its rules, known as General Army Orders, were last revised in 1987. They include the mechanism by which a cessation of violence would come about.
The key IRA committee is the 'army council', which has about eight members and is primarily responsible for directing the IRA campaign. Security sources claim they know almost all its members, said to include associates of the Sinn Fein leaders Gerry Adams and Martin McGuinness.
Members of the army council are elected by the 'army executive', a committee of 12 which in turn is elected by a 'general army convention'. This latter is a large body drawing representatives from each area and department of the IRA. Membership is described in this way: 'The following shall be entitled to attend and vote at the General Army Convention - delegates selected by battalion convention; delegates selected by General Headquarters Staff and Staff of Brigades, Divisions and Commands; two members of the Executive; all members of the Army Council; the Chief of Staff, the Adjutant-General and the Quartermaster-General.'
This convention meets infrequently, partly for reasons of security. Its last known session was in 1986, when it was called to approve a proposal that successful Sinn Fein candidates could take their seats in the Dail in Dublin.
Section 8 of the IRA constitution gives the army council power to 'conclude peace or declare war' on the decision of a majority of council members. But it adds that 'the conclusion of peace' must be ratified by the convention. This means the final decision to call off its campaign cannot be taken by a small group at the head of the organisation, but must have the consent of a majority of senior members.
Several weeks ago, the army council issued a statement saying it had been briefed on and supported the Hume-Adams peace initiative. This was taken in some quarters as meaning it would cease violence if the terms of that initiative were met. A key question now is whether the Major-Reynolds declaration would have the same effect.
Another key question is whether all members of the IRA would obey an order to stop fighting in the event of the army council issuing it and the convention ratifying it. It is not hard to imagine the emergence of diehards who would claim that, even if the rules had been followed, ending the violence would represent a betrayal of the republican cause.
The signs from the republican grass roots are, however, that the rank and file has a great deal of confidence in the leadership of the IRA and Sinn Fein. Some are thought to have wobbled slightly in the light of the recent claim by Sir Patrick Mayhew that Mr McGuinness had contacted the Government and said that 'the conflict was over'. Subsequent disclosures have, however, convinced doubters that Sir Patrick was not telling the truth.