Science fiction (sf) analyses and critiques terraforming by situating theoretical and speculative ideas within wider social, historical and conceptual contexts and by narrating the consequences of specific decisions or frameworks for adapting and colonising celestial bodies. Sf can be used as an experimental forum for developing and scrutinising strategies for projects of planetary dimension. Terraforming sf engages debate about deliberation and the possibility for developing international frameworks for decision making and co-ordination under crisis conditions. This chapter considers Kim Stanley Robinson’s Mars trilogy, Jane Killick’s In the Shadow of Deimos: A Terraforming Mars Novel, Mary Robinette Kowal’s Lady Astronaut trilogy, Andy Weir’s Artemis and Project Hail Mary and Ian McDonald’s Luna trilogy to consider the implications of catastrophe on decision making, the emergence of new institutions that make terraforming possible, the corporate exploitation of space and the importance of the formation of new identities for the persistence of interplanetary colonies.