In 1969, physicist Gerard O’Neill began looking to space colonies as humanity’s new frontier; a decade later, engineer Eric Drexler turned his attention to the molecular world. Blending countercultural ideals with hard science, entrepreneurship, libertarianism, and optimism, these modern utopians predicted their technologies could transform society—but it’s not always easy being a modern utopian. Author W. Patrick McCray examines the successes and pitfalls the scientists encountered, and how they ultimately imagined, designed, and popularized speculative technologies such as space colonies and nanotechnologies