In combat situations prior to Vietnam, U.S. military forces had an existing command and control structure which could be tailored to accomplish the task at hand. In Europe during World War II General Dwight D. Eisenhower modified the command structures developed for the North African and Mediterranean operations to form Supreme Headquarters, Allied Expeditionary Force (SHAEF). After his departure from Bataan in 1942, General Douglas MacArthur had several months in which to design the command structure that ultimately contributed to the defeat of the Japanese. Finally, the U.S. Eighth Army, the dominant command structure controlling all UN forces in combat in Korea, and the General Headquarters, United Nations Command, in Japan, existed prior to the beginning of the Korean War. Such was not the case in Vietnam. There, the command and control arrangements, which ultimately directed a U.S. military force of over 500,000 men, evolved from a small military assistance mission established in 1950. The Military Assistance Advisory Group's philosophy of assistance rather than command significantly influenced the development of the organization. This monograph describes the development of the U.S. military command and control structure in Vietnam. This study is not a conventional military or diplomatic history of the war in Vietnam. Rather, it is an analytical appraisal of the command and control structure.