Mexico City (in Spanish: Ciudad de México, México, D.F., México or simply Méjico) is the capital city of Mexico. It is the most important economic, industrial and cultural center in the country, and the most populous city with 8,836,045 inhabitants in 2008. Consejo Nacional de Población, México; Proyecciones de la Población de México 2005-2050 Accessed on 2008-09-27. Greater Mexico City (Zona Metropolitana del Valle de México) incorporates 59 adjacent municipalities of Mexico State and 1 municipality of the state of Hidalgo, according to the most recent definition agreed upon by the federal and state governments. Consejo Nacional de Población, México; Delimitación de las zonas metropolitanas de México 2005 Accessed on 2008-09-27. In the last national census (2005) Greater Mexico City had a population of 19.2 million people, making it the largest metropolitan area in the western hemisphere and the second largest in the world by population. The estimated population for the Metropolitan Area is 19,826,918 as of 2008. Consejo Nacional de Población, México; Proyecciones de la Población de México 2005-2050 Total projected population of Distrito Federal and the 60 other municipalities of Zona metropolitana del Valle de México, as defined in 2005. Accessed on 2008-09-27. In 2005, it ranked the eighth in terms of GDP (PPP) among urban agglomerations in the world. Along with São Paulo it is the only Beta global city with 8 points in Latin America.

Mexico City is also the Federal District (Distrito Federal in Spanish, and hence the abbreviation D.F.). The Federal District is coextensive with Mexico City: both are governed by a single institution and are constitutionally considered to be the same entity. This has not always been the case. The Federal District, created in 1824, was integrated by several municipalities, one of which was the municipality of Mexico City. As the city began to grow, it engulfed all other municipalities into one large urban area. In 1928, all municipalities within the Federal District were abolished, an action that left a vacuum in the legal status of Mexico City vis-à-vis the Federal District, even though for most practical purposes they were traditionally considered to be the same entity. In 1993, to end the sterile discussions about whether one concept had engulfed the other, or if any of the two entities had any existence in lieu of the other, the 44th Article of the Constitution of Mexico was reformed to clearly state that Mexico City is the Federal District, seat of the Powers of the Union and capital of the United Mexican States.