Human civilization has evolved to the point at which we can consider tapping space resources and expanding beyond Earth’s atmosphere. The Introduction surveys possible motivations for large-scale human emigration to space. Since our early ancestors began to move out of Africa, humans have constantly expanded their range. Today, the pattern of human settlement extends from pole to pole. Humans regularly visit the upper troposphere and ocean floor and technology has enabled a few to even reside above the atmosphere in space stations. For the next few millennia at least (barring breakthroughs), the human frontier will include the solar system and the nearest stars. Will it better to settle the Moon, Mars, or a nearby asteroid and what environments can we expect to find in the vicinity of nearby stars are questions that need to be answered if mankind is to migrate into space. Contents 1. The Old Frontier 2. The New Frontier 3. The Rocket and Its Limits 4. The First "Green" Space Technologies 5. Probes to the Planets: Where we've been on 6. Probes to the Stars: Concept Studies 7. Breaking Out Into Space: Visionary Futures 8. Thinking Interstellar 9. Technological Readiness 10. Space Brakes 11. The Ion Trail 12. The Orbital Steam Locomotive 13. Sky Clippers 14. Art or Science 15. Space Beanstalks 16. Chemical Propulsion for Space Exploration: 17. Human Exploration 18. Defending the Earth 19. Space Miners 20. Some Exotic Possibilities 21. Sights on Centaurus