This paper will focus on the evolution of insurgency and counterinsurgency in Iraq from 2003 - 2009. The Iraq war, split into three periods, reflects the three major evolutions of U.S. counterinsurgency doctrine. The first period 2003-4004, highlights the U.S.’s inability to understand the Iraqi insurgency and implement policies to counter it. The second period, 2005-2006, was a period of decentralization. Some coalition units practiced counterinsurgency techniques during the second period; however, coalition units that practiced counterinsurgency adopted these techniques as they saw fit. This period of decentralization allowed some coalition gains but progress was often short lived. Counterinsurgency was still not implemented across the military, and often new units rotating in did not follow the same counterinsurgency techniques. The final stage, commonly referred to as “The Surge”, centralized counterinsurgency doctrine starting in the beginning of 2007. This centralized counterinsurgency effort has allowed a full transition to Iraq authority. To understand the Iraqi insurgency, I will use a theoretical framework consisting of insurgency doctrine and practice from the Cold War period. Cold War period literature serves as tactical foundation for current insurgent kinetic action. However, unlike the Cold War insurgencies, the Iraqi insurgency was segmented with no overarching political goal other than to remove the coalition troops. To understand the Iraqi insurgency a theoretical framework of “spoiler campaigns” will be developed by combining both Cold War and current insurgent theory. The theoretical framework I will use to explain the counterinsurgency evolution will be based largely on David Galula’s seminal work published on insurgency and counterinsurgency warfare. More contemporary works from David Kilcullen and John Nagl who were instrumental in developing U.S. counterinsurgency operations will also be included to further explain how and why the U.S. military adopted the strategies that it did. The main questions and answers addressed in this work revolve around how and why the Iraqi insurgency and U.S. counterinsurgency developed in the way it did. Additionally, three other questions will be asked from this research. 1) Could the U.S. have done things differently to end the insurgency earlier? 2) Has the U.S. learned enough from the Iraq War to implement counterinsurgency operations in other campaigns? 3) What are the policy implications moving forward, how is the case of Afghanistan different?