In this boldly optimistic manifesto, Savage proclaims a master plan for the human race: to spread life throughout the galaxy. To many, space exploration seems irrelevant to Earth's real problems; but humanity may in fact have no other way to secure its long-term survival. To remain confined to Earth, Savage claims, is to court extinction, possibly within a few decades. Savage (an engineer who has established the Millennial Foundation to promote space exploration) outlines his program for transferring a significant portion of humanity off-planet. The crucial first step is to colonize the ocean surface with floating cities, quadrupling the living space available to the growing population of Earth. This allows us to reverse the degradation of the environment by shifting to the thermal energy of the deep ocean as our primary power source. At the same time, spirulina algae (already on sale in health food stores) becomes a major new food crop. The hardware for these oceanic colonies is already within practical reach: Savage provides a detailed inventory of how his floating cities would work and support themselves, with copious citations of the scientific literature. Once this move is well underway, it frees up energy and resources for the next steps. Improved space vehicles make possible orbiting space colonies, then settlements on the moon. A larger step is terraforming Mars -- creating an atmosphere and a water supply for our lifeless neighbor to form a human habitat. On an even longer time scale, the race can expand into the rest of the solar system: asteroids and the moons of other planets. Ultimately, artificial habitats may completely surround the sun. With the resources of an entire solar system at our command, according to Savage, humanity can at last send out emissaries to other stars. The stuff of science fiction? Of course -- but rigorously built from existing science, carefully documented, and convincingly argued. Highly recommended.