The Occupation of Iraq (2003–2011) was characterized by a large United States military deployment on Iraqi territory, beginning with the US-led invasion of the country in March 2003 which overthrew the Ba'ath Party government of Saddam Hussein and ending with the departure of US troops from the country in 2011. Troops for the occupation came primarily from the United States, the United Kingdom, and Australia, but 29 other nations also provided troops, and there were varying levels of assistance from Japan and other countries, as well as tens of thousands of private military company personnel.

The United States-led invasion of the Republic of Iraq was the first stage of the Iraq War. The invasion began on 19 March 2003 and lasted just over one month, including 26 days of major combat operations, in which a combined force of troops from the United States, the United Kingdom, Australia and Poland invaded Iraq. Twenty-two days after the first day of the invasion, the capital city of Baghdad was captured by coalition forces on 9 April after the six-day-long Battle of Baghdad. This early stage of the war formally ended on 1 May when U.S. President George W. Bush declared the "end of major combat operations" in his Mission Accomplished speech, after which the Coalition Provisional Authority (CPA) was established as the first of several successive transitional governments leading up to the first Iraqi parliamentary election in January 2005. U.S. military forces later remained in Iraq until the withdrawal in 2011.