As forecasts for climate change and its impacts have become more dire, climate engineering proposals have come under increasing consideration and are presently moving toward field trials. This article examines the relevant international environmental law, distinguishing between climate engineering research and deployment. It also emphasizes the climate change context of these proposals and the enabling function of law. Extant international environmental law generally favors such field tests, in large part because, even though field trials may present uncertain risks to humans and the environment, climate engineering may reduce the greater risks of climate change. Notably, this favorable legal setting is present in those multilateral environmental agreements whose subject matter is closest to climate engineering. This favorable legal setting is also, in part, due to several relevant multilateral environmental agreements that encourage scientific research and technological development, along with the fact that climate engineering research is consistent with principles of international environmental law. Existing international law, however, imposes some procedural duties on States who are responsible for climate engineering field research as well as a handful of particular prohibitions and constraints.