A world city, or a world-class city, is a city with a set of somewhat subjective traits which often include the following:

• International familiarity (or "first-name" familiarity – one would say "Paris", not "Paris, France").
• Active influence and participation in international events and world affairs (for example, New York is home to the United Nations headquarters and Brussels is home to NATO headquarters).
• A fairly large population (the center of a metropolitan area with a population of at least one million, typically several million).
• A major international airport that serves as an established hub for several international airlines.
• An advanced transportation system that includes several freeways and/or a large mass transit network offering multiple modes of transportation (subway, light rail, regional rail, ferry, or bus).
• In the West, several international cultures and communities (such as a Chinatown, a Little Italy, or other immigrant communities).
• International financial institutions, corporate headquarters (especially conglomerates), and stock exchanges that have influence over the world economy.
• World-renowned cultural institutions, such as museums and universities.
• A lively cultural scene, including film festivals, premieres, a thriving music or theatre scene; a symphony orchestra, an opera company, art galleries, and street performers.
• A unique cultural air and sophistication produced by its inhabitants.
• Varied retailers and eateries, upscale boutiques and hotels, and a thriving nightlife.
• Beautiful natural setting, landmarks, and specific tourist destinations.
• Hosted international sporting events such as the Olympics or the World Cup.

Several powerful and influential media outlets with an international reach are based in the world cities, such as the BBC, The New York Times, Le Monde, The Chicago Tribune, The Times, and Pravda.

In the Western World, New York, London, and Paris have been traditionally considered the "big three" world cities – not incidentally, they also serve as symbols of global capitalism. Also, Tokyo can be added to the top of the list, due to the influence of Japan in world economic affairs. However, many people have a personal list, and any two lists are likely to differ based on cultural background, values, and experience.

In certain First World countries, the rise of suburbia and the ongoing migration of manufacturing jobs to Third World countries has led to significant urban decay. Therefore, to boost urban regeneration, tourism, and revenue, the goal of building a world-class city has recently become an obsession with the governments of some mid-size cities and their constituents.

The phenomenon of world-city building, albeit with slightly more success, has also been observed in Sydney, Buenos Aires, Frankfurt, and Toronto: each of these cities has emerged as large and influential.

GaWC Inventory of World Cities

An influential attempt to define and categorise world cities was made by the Globalization and World Cities Study Group & Network (GaWC) [1], based primarily at Loughborough University. The roster was outlined in the GaWC Research Bulletin 5 [2] and ranked cities based on their provision of "advanced producer services" such as accountancy, advertising, banking/finance and law. The Inventory identifies three levels of world city, termed Alpha, Beta and Gamma for their relative influence. Each level contains two or three sub-ranks. There is also a fourth level of cities that show potential to become world cities in the future. This classification is not yet authoritative, but is certainly useful as a starting point for discussion.

The Alpha (most influential) world cities were divided into two sub-ranks:

• 12 points: London, Paris, New York, Tokyo

• 10 points: Chicago, Frankfurt, Hong Kong, Los Angeles, Milan, Singapore

There is a schematic map of the GaWC cities at their website, [3], which shows clearly that the great majority of their defined cities lie in the Northern Hemisphere. The GaWC is a somewhat subjective ranking, as is any other, but the top four listed cities at least match those commonly considered the major world cities.