Because of its transboundary effects and because states will be the primary actors, large-scale solar geoengineering and its governance are matters of international relations. The divergent problem structures among the responses to climate change help explain extant and likely action. Abatement and negative emissions technologies are aggregate effort global public goods and consequently undersupplied. Solar geoengineering would be a single best effort and a mutual restraint global public good, implying that it might be oversupplied. Uni- or minilateral deployment would be a problem if it were premature or contrary to the international community’s consensus. Solar geoengineering could pose other challenges to international relations such as legitimate decision-making, potential disagreements, cost-sharing, and security risks. Its sudden and sustained termination would have severe negative environmental impacts, but the probability of this is uncertain and may be low. Some economists have explicitly modeled states as rational actors to understand, explain, and predict their behavior in this domain. Given the approach’s limitations, these results should be interpreted with caution.