This thesis examines the conduct of the US Army's counterinsurgency campaign in Iraq from the end of May 2003 through March 2004. While examining how the US Army is implementing existing counterinsurgency (COIN) doctrine, this thesis also addresses the topics of what the doctrine is and where it came from. The thesis will also make recommendations for improvement. The thesis includes five chapters beginning with a brief introduction, followed by a review of the literature pertaining to US COIN doctrine, the doctrine of other nations, and the background of Iraq. A look at the history of the US COIN doctrine development through US Army operations overseas follows. Current US Army operations in Iraq are examined next, based off of interviews with participants, news reports, and reports from the Center for Army Lessons Learned. The last chapter examines how doctrine fails to adequately address the role of US forces as an occupation authority and makes recommendations. Basic principles outlined in US doctrine are still applicable, but US and coalition forces are not applying them as intended: unifying their military efforts with a comprehensive economic, social, and political reform plan.