Notions of the impending climate crisis have pushed a set of highly contested techno-scientific measures onto policy agendas around the world. Suggestions to deliberately alter, to engineer, the Earth’s climate have gained political currency in recent years not as a positive vision of techno-scientific innovation, but as a daunting measure of last resort. The controversial status of various so-called climate engineering proposals raises a simple, yet pressing question: How has it has come to this? And, more specifically, how did such contested measures earn their place on policy agendas, despite enormous scientific complexities and fierce political contestation? Global societal problems, such as climate change, financial crises, or pandemics have brought the political relevance of scientific expertise to the foreground. This book speaks to scholarship in sociology and science studies, seeking to illuminate the essential entanglements between efforts to understand and efforts to govern such problems. By giving climate engineering a life of its own and following its dynamic trajectory as a contested object of expert work, this book sheds light on the reflexive and historically contingent interplay of science and politics as two distinct, yet increasingly interdependent, realms of society.