Mexico City (in Spanish: Ciudad de México, México, D.F., or simply México ) 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 8,720,916 inhabitants in 2005. Greater Mexico City (Zona Metropolitana del Valle de México) incorporates 58 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. In 2006 Greater Mexico City had a population of 19.2 million, making it the largest metropolitan area in the western hemisphere and the second blank">Síntesis de Resultados del Conteo 2005 INEGI or third largest in the world. In 2005, it ranked the eighth in terms of largest GDP (PPP) among urban agglomerations in the world.

Mexico City is also the Federal District (Distrito Federal in Spanish, and hence the abbreviation D.F. that officially follows the name of the city). 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.

Mexico City is located in the Valley of Mexico, also called the Valley of Anáhuac, a large valley in the high plateaus at the center of Mexico, at an altitude of 2,240 meters (7,349 feet). It was originally built by the Aztecs in 1325 on an island of Lake Texcoco. The city was almost completely destroyed in the siege of 1521, and was redesigned and rebuilt in the following years following the Spanish urban standards. In 1524 the municipality of Mexico City was established, known as México Tenustitlán, and as of 1585 it is officially known as Ciudad de México.