A global phenomenon, suburbanization entails low-density settlement at the urban fringe. It is caused especially by urbanization, improved transportation, job decentralization, public policy, and a common preference for suburban living. Most suburbs are developed by private agents guided by the state; in the global South many are produced informally by squatters or ‘pirate’ developers. They take many forms: residential, industrial, mixed; exurban/peri-urban, outer, inner; polycentric, dispersed; planned, unplanned; elite, middle class, low income; and ethnic. Arguably, they reflect and influence suburbanism, a private, family-focused way of life. Surbanization is necessary, and reduces housing costs, but entails major public and private expenditures, reduces farmland, and disrupts ecosystems.