Science fiction (SF) emerges as a distinct literary and cultural genre out of a familiar set of world-famous texts ranging from Mary Shelley’s Frankenstein (1818) to Gene Roddenberry’s Star Trek (1966–) to the Marvel Cinematic Universe (2008–) that have, in aggregate, generated a colossal, communal archive of alternate worlds and possible future histories. SF’s dialectical interplay between utopian optimism and apocalyptic pessimism can be felt across the genre’s now centuries-long history, only intensifying in the 20th century as the clash between humankind’s growing technological capabilities and its ability to use those powers safely or wisely has reached existential-threat propositions, not simply for human beings but for all life on the planet. In the early 21st century, as in earlier cultural moments, the writers and critics of SF use the genre’s articulation of different societies and different possible futures as the occasion to reflect on our own present, in ways that range from full-throated defense of the status quo to the ruthless denunciation of all institutions that currently exist in the name of some other, better world. SF’s global popularity has grown to the point where it now looms quite large over cultural production generally, becoming arguably the most popular narrative genre in existence, particularly in the sorts of SF action spectacles that have dominated the global box office of the first two decades of the 21st century. It has also become increasingly difficult to tell the difference between the things we used to think of as SF and the advanced communication, transportation, and entertainment technologies that have become so ubiquitous and familiar that we now take them for granted, as well as the growing prevalence of political, economic, and ecological crises now erupting out of the pages of our science fictions, like our very worst dreams come to life.