These are the key events that happened before, during and after the controversial US-led invasion.
September 11 2001: Terrorist attacks
Al-Qaeda terrorists launch attacks on New York's World Trade Center and other US east coast targets using hijacked planes.
Some 2,996 people are killed.
September 12 2001: UK pledges support to US
The then-prime minister Tony Blair promises George W Bush that the UK will support the US in whatever course of action it decides to take.
October 2001: Aerial attacks begin
A US-led coalition begins aerial attacks on Afghanistan, ultimately leading to the overthrow of the Taliban.
March 2002: Jack Straw issues warning
Jack Straw, then foreign secretary, warns Tony Blair that invading Iraq would raise legal questions.
April 2002: MI6 casts doubt on immediacy of Iraq threat
MI6 briefs Tony Blair that the threat of weapons of mass destruction from Libya is far more serious that that from Iraq.
April 2002: Blair meets Bush
Tony Blair meets George W Bush at his Crawford ranch in Texas, after which Mr Blair stance on Iraq was reported to have "tightened".
However, the former prime minister denied reports that he took an "undertaking in blood" to invade Iraq.
September 2002: The Iraq War dossier
The government publishes a dossier featuring the controversial claim that Saddam Hussein could launch weapons of mass destruction within 45 mins.
October 2002: Congress authorisation
The US Congress authorises President Bush to use military force against Iraq.
February 2003: Iraq War protests
Hundreds of thousands of people took to the streets of London to protest against military action in Iraq.
Police said it was the UK's biggest ever demonstration, with at least 750,000 people taking part.
Organisers put the figure closer to two million.
March 2003: Missile attacks begin in Iraq
US-led campaign to topple Iraq's leader Saddam Hussein begins with missile attacks in Baghdad.
Some 46,000 British troops are deployed in Iraq as part of the military action - one the largest deployment of British troops since the Second World War.
May 2003: Bush's 'Mission Accomplished speech'
President Bush delivers his now-infamous "Mission Accomplished" aboard an aircraft carrier.
He says "major combat operations in Iraq have ended” and that “in the battle of Iraq, the United States and our allies have prevailed".
June 2003: Short says Blair misled Cabinet
Former International Development Secretary Clare Short says in a BBC interview that Tony Blair misled the Cabinet on the eve of the war.
July 2003: David Kelly found dead
Biological warfare expert Dr David Kelly is found dead.
Dr Kelly had been named as the source of quotes used by former BBC journalist Andrew Gilligan to suggest that the dossier used to justify the Iraq invasion has been "sexed up".
October 2003: Report shows no WMD evidence in Iraq
A report from the Iraq Survey Group reveals that there is no evidence of weapons of mass destruction in Iraq.
December 2003: Saddam Hussein captured
Saddam Hussein is captured after nine months in hiding.
April 2004: US military abuse made public
US broadcaster CBS publicises photographic evidence of abuse perpetrated by US forces against prisoners in Baghdad’s Abu Ghraib prison.
July 2004: US Senate criticises war in Iraq
A senate report says the US and its allies went to war in Iraq on "flawed" information.
December 2005: Sadaam Hussein is executed
Saddam Hussein is hanged at an undisclosed location in Baghdad after dominating Iraq for nearly 25 years.
May 2006: Terrorist charged over September 11 attacks
Self-confessed al-Qaeda conspirator Zacarias Moussaoui is sentenced to life in jail over the September 11 attacks.
May 2006: New government in Iraq
A new Iraqi government succeeds the transitional government, which received sovereignty of the Coalition Provisional Authority in 2004.
January 2007: US boosts military presence in Iraq
The US announces that 20,000 extra troops will be deployed in Iraq to increase security in Baghdad.
May 2009: British troops leave Iraq
The last British combat troops leave Iraq after most withdraw from Basra earlier in the year in July.
Tens of thousands of Iraqi civilians also died.