A pathbreaking history of the regulatory foundations of America's twentieth-century aerial preeminence. Today, the federal government possesses unparalleled authority over the atmosphere of the United States. Yet when the Wright Brothers inaugurated the air age on December 17, 1903, the sky was an unregulated frontier. As increasing numbers of aircraft threatened public safety in subsequent decades and World War I accentuated national security concerns about aviation, the need for government intervention became increasingly apparent. But where did authority over the airplane reside within America's federalist system? And what should US policy look like for a device that could readily travel over physical barriers and political borders? In Sovereign Skies, Sean Seyer provides a radically new understanding of the origins of American aviation policy in the first decades of the twentieth century. Drawing on the concept of mental models from cognitive science, regime theory from political science, and extensive archival sources, Seyer situates the development, spread, and institutionalization of a distinct American regulatory idea within its proper international context. He illustrates how a relatively small group of bureaucrats, military officers, industry leaders, and engineers drew upon previous regulatory schemes and international principles in their struggle to define government's relationship to the airplane. In so doing, he challenges the current domestic-centered narrative within the literature and delineates the central role of the airplane in the reinterpretation of federal power under the commerce clause. By placing the origins of aviation policy within a broader transnational context, Sovereign Skies highlights the influence of global regimes on US policy and demonstrates the need for continued engagement in world affairs. Filling a major gap in the historiography of aviation, it will be of interest to readers of aviation, diplomatic, and legal history, as well as regulatory policy and American political development.