Mexico City (in Spanish: Ciudad de México, D.F., Distrito Federal, or México)[1] 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.[2] 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.[3] Greater Mexico City has a population exceeding 22 million people,[4] 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.[5] [6] In 2005, it ranked the eighth in terms of GDP (PPP) among urban agglomerations in the world.[7] 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.[8]

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.[9]

According to a study[7][10] conducted by PricewaterhouseCoopers, Greater Mexico City (with a population of 19.2 million) had a GDP of $315 billion in 2005 (at purchasing power parity), ranking as the eighth-richest urban agglomeration in the world after the greater areas of Tokyo, New York, Los Angeles, Chicago, Paris, London and Osaka/Kobe, and the richest in Latin America; in 2020 it is expected to rank seventh with a $608 billion GDP, displacing Osaka/Kobe.

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 ft). It was originally built as Tenochtitlan 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,[11] and as of 1585 it is officially known as ciudad de México.[11]