Abstract
Airspace is a component of every nation's sovereign territory, but its upper border is uncertain. This article assesses the prospects for height limits to be created for airspace as increasing high-altitude human activity leads to events that will require jurisdiction to be determined. Taking the notion of an upper boundary to airspace, the paper develops a description of nations as three-dimensional territorial constructs. Among the implications of this would be a multiplication of state borders and border phenomena, and the potential for nations to be adjacent to each other vertically as well as horizontally.