Outer space is becoming a more accessible and less expensive domain in which to operate. Consequently, growing numbers of state and non-state actors (NSAs) are operating in, to, and through space. At the same time, instances of space-based and ground-based interference with space systems are also increasing, disrupting crucial space-supported services and applications relied on by millions, with great financial and operational costs. The increased participation of NSAs in space activities raises particular concerns, especially the threat of intentional interference with space systems by nefarious actors like terrorist organizations. It also requires consideration of whether states bear responsibility and/or liability for the acts of NSAs with a nexus to those states. At first glance, it is tempting to conclude that one or more normative legal regimes would apply. The potential regimes include international space law, international telecommunications law, and the law of state responsibility. On further examination, however, when it comes to interference, there appears to be no effective legal mechanism to hold states accountable for NSA interference with space systems, which can be exploited by NSAs and challenge efforts by states to enforce “good” behaviour.