This article offers a descriptive and normative economic analysis of international environmental rights. States, sovereignty, international negotiations, and international law resemble legal persons, property, the market, and private law, respectively. Just as the initial entitlement of persons’ property rights is important to increasing welfare when transaction costs are significant, so too is that of states’ sovereignty rights, including those regarding the environment. What is the initial entitlement of these rights? Is this relatively efficient? How are these rights protected? The article considers three possible initial entitlements. First, states’ right to cause transboundary environmental harm and, second, their right to be free therefrom are each rejected due to weak theoretical support and insufficient state practice. These initial entitlements would also be less efficient. In contrast, an initial entitlement consisting of both the prevention of transboundary harm and the equitable use of shared natural resources is supported by theory and practice. This entitlement appears relatively efficient, and the relevant legal instruments reveal an implicit underlying economic logic. These international environmental rights are generally protected by mechanisms that resemble liability.