Geoengineering describes a range of techniques that are proposed to counteract some of the negative impacts of climate change at a global scale, without actually reducing emissions. This chapter provides an overview of geoengineering techniques and the existing international law applicable to them. Geoengineering techniques are not as such prohibited and are hardly addressed by international law. They pose fundamental challenges to a potentially emerging area of international climate law. The main challenge for policy makers is deciding whether and how to get involved without providing an incentive or excuse for stepping away from reducing emissions. A key component is to clearly separate scientific input and political decision-making.