Space activities and infrastructure today are critical to international security and the global economy. The space domain is not, however, subject to sovereign control by international law. Like other shared domains, such as the high seas, the polar regions, and arguably cyberspace, space is a domain in which State and non-State actors interact beyond national borders. Given global dependence on space-derived information and an increase in potential adversary threats to space assets, States have taken a number of steps in recent years to protect their national interests in space. Despite its importance and increasing global attention, international cooperation and competition in space is a relatively under theorized topic in international relations. Conversely, international relations theories are not widely used in the development of United States (U.S.) national space policy and the practice of space diplomacy, from a U.S. perspective. The intent of this article is to address this rift between theory and policy by briefly describing major theories of international relations and where they can shed light on how and why States engage in cooperation and competition in space. The article addresses the major schools of realism, liberalism, and constructivism, with applications to space activity. No single theory fully describes the U.S. policy approach to international space activities. Different theories, applied to the same situation, can, however, provide useful perspectives to both theorists and policy-makers. This suggests the use of a mixed, pragmatic approach, referred to as "eclectic theorizing" in international relations literature, as a promising avenue for further research.& COPY; 2022 Elsevier Ltd. All rights reserved.
