The Introduction to Earthopolis: A Biography of Our Urban Planet outlines large themes in the 6,000-year story of how cities gave humans the power to dominate Earth. Our Urban Planet is at once a plural and a singular phenomenon. Its diversity reflects the many birthplaces and birthdates of cities on six continents over six millennia, yet it has become a connected city-enabled habitat of a single species on a single planet. Cities – compact built spaces that rely on many other, dispersed ones – allowed us to harvest enough energy from the Sun and Earth to create the political communities, institutions, wealth, and ideas we needed to act on a global scale, to build an Earth-encrusting habitat, to impact all other parts of our planet’s biosphere, and to face the consequences. The life of Earthopolis exists in space and time. As our urban harvests of natural energy transformed throughout global urban history, from river valleys to the world ocean, and then to hydrocarbon, the geographic extent of our Urban Planet’s four defining realms – of human action, habitat, impact, and consequence – expanded and retreated across Earth. Now our Urban Planet puts us in perilous command of our host planet’s entire halo of life.