The National Security Council was established by the National Security Act of 1947, can be regarded as one of the most important revolutionary in American government. The Council not only serves as the main actor in coordinating foreign and defense policies among various government agencies, but also President’s principal advisor. This thesis focuses and analyzes the coordinating function of NSC by looking at its interrelations with Department of State, Department of Defense, and Central Intelligence Agency. Furthermore, by studying the case of 911 and Iraq War, this thesis try to find out the coordinating function the NSC play in the decision making process.