As negotiations aimed at improving our global response to climate change continue to falter, geoengineering - the planetary scale engineering of the climate system - is expected to receive increasingly serious consideration by states seeking ways to manage the most dangerous risks of climate change. Agreeing on a governance framework in which even serious research into geoengineering technologies can take place presents an immense international political challenge. In this important book, a collection of experts from the domains of science, science policy, politics, law, governance, ethics and civil society provide the essential foundation on which the debate can be built. Opening with an introduction to geoengineering and the main technological options currently on the table, the book then moves on to examine the ethical dilemmas and governance challenges posed. All actors involved in the emerging debate about geoengineering technologies need to understand not only the climate science and uncertainties underpinning these technological ideas, but also the possible ramifications of geoengineering for human societies. This includes an appreciation of the precedents for governing transboundary/global issues and how far lessons learnt from these precedents can be applied to the special case of geoengineering. The book closes by presenting a range of short commentaries from engaged scientists and policymakers, NGOs, corporations and researchers from developed and developing countries, as well as a set of key documents from already emerging debates. In sum, this book provides an indispensable resource for scientists, activists, policymakers and political figures aiming to engage in the geoengineering debate.