Mexico City (Spanish: Ciudad de México), Mexico, the nation's capital and most populous city. Its popular Mexican name is simply Mexico. The city is coextensive with Mexico's Federal District. It is one of the great metropolises of the world and one of the most rapidly growing.

Mexico City lies in a mountain-rimmed basin, called the Valley of Mexico, some 500 miles (800 km) south of the United States border. It is one of the world's loftiest cities; the heart of the city has an elevation of about 7,350 feet (2,240 m) above sea level. It is built largely on land reclaimed by draining and filling old Lake Texcoco, site of Tenoch-titlán, the island capital of the Aztec Empire and the nucleus of the present city.

Along with the dynamic growth of the past several decades have come multiple urban problems. Among them are extremely high unemployment among the millions of new residents, widespread slums, massive traffic congestion, and severe air pollution. An old problem, still unresolved, is the gradual settling of the old lake bed, on which the city is built, and the steady sinking of many buildings.