A report into the intelligence which the British government had about Iraq and weapons of mass destruction is to be published on Wednesday 14 July. It has been written by a committee headed by the former head of the civil service Lord Butler. BBC News Online examines some of the issues:
Why was the inquiry set up?
The Foreign Secretary Jack Straw set up the inquiry on 4 February 2004 following widespread public concern about the reliability of pre-war intelligence which claimed that Iraq had weapons of mass destruction. No such weapons have been found.
The inquiry members are: Lord Butler; Sir John Chilcot, a former civil servant in Northern Ireland; Labour MP Ann Taylor; Conservative MP Michael Mates; and Field Marshal Lord Inge, formerly Chief of the Defence Staff.
The committee met in private but had access to witnesses and documents.
What were its terms of reference?
It had three tasks. The first was to assess what intelligence is available about WMD and "countries of concern." This means not just Iraq but also countries like North Korea and Iran. The idea behind this was to see if problems encountered over Iraq might also occur elsewhere.
The second - the one attracting the most interest - was to "investigate the accuracy of intelligence on Iraqi WMD up to March 2003." March 2003 is when the war started. The inquiry had to "examine any discrepancies" between the pre-war intelligence and what has been found (or not found) since.
Thirdly, it had to make recommendations about the future handling of intelligence on WMD in "countries of concern."
What questions need to be answered?
The broad questions include: Were the sources for intelligence reliable and properly checked, did the government accept what it was being told too easily and why was it so forthright in its dossier on Iraq issued in September 2002.
Specifically, people will want to know, among other things, on what basis the government claimed that Iraq had chemical and biological weapons and was aiming to develop a nuclear bomb, why it said that Saddam Hussein had weapons he could fire within 45 minutes, why it said that Iraq had tried to get uranium from Niger in Africa and why it claimed that he had a number of Scud missiles.
Is the inquiry likely to conclude there was failure of intelligence?
This is the expectation because no weapons of mass destruction have been found.
It will be interesting to compare its findings with that of the Senate Intelligence Committee in the United States, which has concluded that there was indeed a major failure of intelligence.
On the other hand, the House of Commons Committee on Intelligence and Security in a report last September was generally supportive of the intelligence community and of the government's position, though it was critical of some important details.
Two members of that committee, its chair Ann Taylor, a Labour MP, and the conservative MP Michael Mates, are on the Butler inquiry.
Mr Mates revealed that the Butler report would deal with the theme that "intelligence does have its limitations."
Will the inquiry name names?
This remains to be seen.
The names people will be looking for fall into two categories - politicians and intelligence officials.
The roles of the Prime Minister Mr Blair, the Foreign Secretary Mr Straw and the Defence Secretary Mr Hoon in accepting the intelligence are likely be examined.
It has also been reported that the Attorney general, Lord Goldsmith, who issued a legal ruling approving the war, will be mentioned.
The intelligence officials include John Scarlett, who was head of the Joint Intelligence Committee at the time (and has since been appointed head of the Secret Intelligence Service MI6) and Sir Richard Dearlove, head of M16 at the time.
Lord Butler himself has been criticised. Why?
His critics say that as a former top civil servant he is too close to government and will not rock the boat. They point to his too ready acceptance in 1994 of former Tory MP Jonathan Aitken's word about his dealings with a Saudi businessman. In fact Mr Aitken had lied and was later sent to prison for perjury.
His supporters say that his knowledge of government will help him make accurate assessments.
What's the difference between the Butler and the Hutton inquiries?
Lord Hutton dealt with the death of the government scientist Dr David Kelly, the BBC's role and the government's published dossier on Iraqi weapons. Lord Hutton deliberately did not get into the actual intelligence, only what use was made of it. The Butler inquiry is looking into the intelligence itself.
Have the Americans set up a similar inquiry?
On 6 February 2004, shortly after the Butler inquiry was announced, President Bush appointed a bipartisan panel to make a similar assessment of US intelligence and Iraq. It is headed by former Senator Chuck Robb, a Democrat and a former Appeal Court judge Laurence Silberman who served two Republican presidents.
This commission is not due to report until next year, after the US presidential election.
It is separate from the Senate Intelligence Committee which has published its own very critical findings.