A metropolitan area or metro is a region consisting of a densely populated urban agglomeration and its surrounding territories which share industries, commercial areas, transport network, infrastructures and housing. A metropolitan area usually comprises multiple principal cities, jurisdictions and municipalities: neighborhoods, townships, boroughs, cities, towns, exurbs, suburbs, counties, districts and even states and nations in areas like the eurodistricts. As social, economic and political institutions have changed, metropolitan areas have become key economic and political regions.

In the United States, metropolitan areas are delineated around the core of a core based statistical area, which is defined as an urban area and includes central and outlying counties. In other countries metropolitan areas are sometimes anchored by one central city such as the Paris metropolitan area (Paris). In other cases, metropolitan areas contain multiple centers of equal or close to equal importance, especially in the United States; for example, the Dallas–Fort Worth metropolitan area has eight principal cities. The Islamabad–Rawalpindi metropolitan area in Pakistan, the Rhine-Ruhr in Germany, and the Randstad in The Netherlands are other examples.

In the United States, the concept of metropolitan statistical areas has gained prominence. The area of the Greater Washington metropolitan area is an example of statistically grouping independent cities and county areas from various states to form a larger city because of proximity, history, and recent urban convergence. Metropolitan areas may themselves be part of a greater megalopolis. For urban centres located outside metropolitan areas that generate a similar attraction at a smaller scale for a region, the concept of a regiopolis and a respective regiopolitan area, or regio, was introduced by German professors in 2006. In the United States, the term micropolitan statistical area is used.

A metropolitan area combines an urban agglomeration with the contiguous built-up areas, which are not necessarily urban in character but are closely bound to the center by employment or other commerce. These outlying zones are sometimes known as a commuter belt and may extend well beyond the urban zone to other political entities. For example, East Hampton, New York, on Long Island is considered part of the New York metropolitan area.

In 2020, the European Commission, the Food and Agriculture Organization, the United Nations Human Settlements Programme, the International Labour Organization, the OECD, and the World Bank have agreed on a common methodological framework for delimitation of urban and rural areas, which contains a definition of metropolitan areas called the Functional urban area. It is defined as a city and its commuting zone, which is a contiguous area of spatial units that have at least 15% of their employed residents working in the city.

In practice, the parameters of metropolitan areas, in both official and unofficial usage, are not consistent. Sometimes they are little different from an urban area, and in other cases, they cover broad regions that have little relation to a single urban settlement; comparative statistics for metropolitan areas should take this into account. The term metropolitan can also refer to a county-level municipal government structure, with some shared services between a central city and its suburbs, which may or may not include the entirety of a metropolitan area. Population figures given for one metro area can vary by millions.

There has been no significant change in the basic concept of metropolitan areas since its adoption in 1950, although significant changes in geographic distributions have occurred since then, and more are expected. Because of the fluidity of the term "metropolitan statistical area", the term used colloquially is more often "metro service area", "metro area", or "MSA", taken to include not only a city but also the surrounding suburban, exurban and sometimes rural areas, all of which the city is presumed to influence. A polycentric metropolitan area contains multiple urban agglomerations not connected by continuous development. In defining a metropolitan area, it is sufficient that a city or cities form a nucleus with which other areas have a high degree of integration.

A metropolitan area is commonly known and characterized by a high concentration in service sector labor and enterprises. Macroeconomics views metropolitan areas as trade regions of economic significance.