Ask an American intelligence officer to tell you when the country started doing modern intelligence and you will probably hear something about the Office of Strategic Services in World War II or the National Security Act of 1947 and the formation of the Central Intelligence Agency. What you almost certainly will not hear is anything about World War I. In World War I and the Foundations of American Intelligence, Mark Stout establishes that, in fact, World War I led to the realization that intelligence was indispensable in both wartime and peacetime. After a lengthy gestation that started in the late nineteenth century, modern American intelligence emerged during World War I, laying the foundations for the establishment of a self-conscious profession of intelligence. Virtually everything that followed was maturation, reorganization, reinvigoration, or reinvention. World War I ushered in a period of rapid changes. Never again would the War Department be without an intelligence component. Never again would a senior American commander lead a force to war without intelligence personnel on their staff. Never again would the United States government be without a signals intelligence agency or aerial reconnaissance capability. Stout examines the breadth of American intelligence in the war, not just in France, not just at home, but around the world and across the army, navy, and State Department, and demonstrates how these far-flung efforts endured after the Armistice in 1918. For the first time, there came to be a group of intelligence practitioners who viewed themselves as different from other soldiers, sailors, and diplomats. Upon entering World War II, the United States had a solid foundation from which to expand to meet the needs of another global hot war and the Cold War that followed.