Solar geoengineering holds the potential for both benefit and harm. Actors such as states could ask ex ante for assurances of compensation, possibly as a precondition for not opposing the activity, or demand ex post compensation for actual or claimed harm. Legal rules could indicate that those who conducted or approved an activity would be liable to pay damages. There could be a basis – at least in principle – in customary international law for state liability for transboundary harm caused by solar geoengineering that was contrary to international law. Although space-based solar geoengineering is presently prohibitively expensive, states would be strictly liable for harm arising from it. Compensation for other potential harm would face substantial political, institutional, and theoretical challenges, including what damages to compensate, the injurers’ and victims’ identities, and mechanisms and reasons for securing compensation. While recognizing states’ strong resistance to compensation, the chapter suggests an international compensation fund for harm from large-scale outdoor solar geoengineering research and offers initial thoughts regarding that from deployment.