From the start of operations in Iraq in March 2003 until mid-2009, ground troops from thirty-seven countries fought at the side of U.S. forces, with many more providing indirect support and assistance. These countries furnished significant military aid to the United States Army and performed vital missions relevant to combat, intelligence, reconstruction, and support operations. The participation of these coalition partners proved critical to the success of the overall mission. Allied Participation in Operation Iraqi Freedom examines the achievements and contributions of the allied nations that supplied ground troops to the U.S.-led coalition in Iraq during 2003-2009. It does not cover forces deployed to Iraq under the aegis of the United Nations or the North Atlantic Treaty Organization. The U.S. military's experience in Operation IRAQI FREEDOM reconfirms the necessity of coalition building in modern warfare, even when the U.S. Army and Marine Corps ground forces shoulder the largest burden. This monograph offers separate sections on each coalition ally and presents basic information about deployed military forces and their general operational experiences in Iraq. It also provides a framework for more detailed histories to follow.