A global city (also called world city or sometimes alpha city or world center) is a city generally considered to be an important node in the global economic system. The concept comes from geography and urban studies and rests on the idea that globalization can be understood as largely created, facilitated and enacted in strategic geographic locales according to a hierarchy of importance to the operation of the global system of finance and trade.

The most complex of these entities is the "global city", whereby the linkages binding a city have a direct and tangible effect on global affairs through socio-economic means. The terminology of "global city", as opposed to megacity, was popularized by the sociologist Saskia Sassen in reference to her 1991 work, "The Global City: New York, London, Tokyo" though the term "world city" to describe cities which control a disproportionate amount of global business dates to at least May 1886, to a description of Liverpool by the Illustrated London News. Patrick Geddes also used the term "world city" later in 1915. Cities can fall from such categorization, as in the case of cities that have become less cosmopolitan and less internationally renowned in the current era, e.g., Kaliningrad, Russia; Thessaloniki, Greece; and Alexandria, Egypt.