This publication sets out the report of the inquiry by the five-member committee, chaired by Lord Butler, established in February 2004 to examine the quality of intelligence used as justification for UK military participation in the war against Iraq in March 2003. The inquirys remit was: i) to investigate discrepancies in the gathering, evaluation and use of intelligence on Iraqi weapons of mass destruction (WMDs) (including the September 2002 intelligence dossier which alleged Iraq was capable of deploying WMDs within 45 minutes), given the subsequent failure by the Iraq Survey Group to find WMDs in Iraq; and ii) to make recommendations for future practice, in the light of the difficulties of operating in countries of concern. The report focuses on structures, systems and processes rather than on the actions of individuals. Issues discussed include: the nature and use of intelligence; countries of concern other than Iraq and global trade; international terrorism and intelligence responses; counter-proliferation machinery; Iraqs WMD programmes since 1990 and intelligence assessments; the role of intelligence in assessing the legality of the war; validation of human intelligence sources; the links between Al Qaida and the Iraqi regime; the intelligence machinery including the work of the Defence Intelligence Staff (DIS) and the Joint Intelligence Committee (JIC), and the machinery of government.