Mexico City (in Spanish: "Ciudad de México", "D.F." (stands for "Distrito Federal") or "México is the capital city of Mexico. It is the most important economic, industrial, and cultural center in the country; the most populous city with over 8,836,045 inhabitants in 2008. Consejo Nacional de Población, México; Proyecciones de la Población de México 2005-2050. Retrieved 2008-09-27. Greater Mexico City (Zona Metropolitana del Valle de México) incorporates 59 adjacent municipalities of Mexico State and 29 municipalities of the state of Hidalgo, according to the most recent definition agreed upon by the federal and state governments. Secretaria de Desarrollo Metropolitano, México; Delimitación de la Zona Metropolitana del Valle de México. Retrieved 2009-02-20. Greater Mexico City has a population exceeding 22 million people, Mexcio City Government. Retrieved 2009-02-20. making it the largest metropolitan area in the western hemisphere and the second largest in the world by population according to the United Nations and other organizations. United Nations 2007 Revision Population Database. Retrieved 2009-03-01. CityMayors World's Largest Cities and Urban Areas in 2006. Retrieved 2009-03-01. In 2005, it ranked the eighth in terms of GDP (PPP) among urban agglomerations in the world. Aside from São Paulo it is the only Beta global city with 8 points in Latin America and ranked 25th among global cities by Foreign Policy's 2008 Global Cities Index.

Mexico City is also the Federal District (Distrito Federal in Spanish, and hence the abbreviation D.F.). The Federal District is coexistent 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.