Geoengineering provides new possibilities for humans to deal with dangerous climate change and its effects but at the same time creates new risks to the planet. This book responds to the challenges geoengineering poses to International Law by identifying and developing the rules and principles that are aimed at controlling the risks to the environment and human health arising　from geoengineering activities, without neglecting the contribution that geoengineering could make in preventing dangerous climate change and its impacts. It argues first that the employment of geoengineering should not cause significant environmental harm to the areas beyond the jurisdiction of the state of origin or the global commons, and the risk of causing such harm should be minimized or controlled. Second, the potential of geoengineering in contributing to preventing dangerous climate change should not be downplayed.