Cádiz is a coastal city in southwestern Spain, in the region of Andalusia, and is the capital of the province of Cádiz. As of the 2003 census its population was 134,989, and the population of the entire urban area was estimated to be 406,095, ranking as the 16th-largest urban area of Spain.

The city was originally founded as Gadir (Phoenician גדר "walled city") by the Phoenicians, who used it in their trade with Tartessos. The Greeks knew it as Gadira or Gadeira. Traditionally, its date of establishment is about 1100 BCE, although as of 2004 no finds have been found that date back further than the 9th century BCE. It is regarded as the most ancient still existing city in western Europe. According to Greek legend, Gadir was founded by Heracles after killing Geryon. Indeed, one of its notable features during this era was the temple dedicated to the Phoenician god Melqart. Some historians think that the columns of this temple gave origin to the myth of the Columns of Hercules (Melqart was associated by the Greeks with Heracles, or Hercules).

In about 500 BCE the city fell into the hands of the Carthaginians. In the 3rd century BCE, the Romans conquered the city and renamed it Gades. The city flourished under Roman rule, but, with the decline of the Roman Empire , Gades' commercial importance began to fade.

Under Moorish rule, the city was called Qādis (Arabic قادس), and the modern Spanish name Cádiz was derived from this form.

During the Age of Exploration the city had another renaissance: Columbus sailed from Cádiz on his second voyage in 1495, and the city later became the home port of the Spanish treasure fleet.

Sir Francis Drake destroyed a Spanish fleet in its harbor in April 1587. In the Anglo-Spanish War Admiral Robert Blake blockaded Cádiz from 1655 and 1657, during which one of his captains, Richard Stayner destroyed most of the Spanish treasure fleet. A galleon of treasure was captured, and the overall loss to Spain was estimated at £2,000,000.

In the 18th century, the city surpassed Seville as the port monopolizing commerce with Spanish America.

Cádiz was the seat of the liberal Cortes fighting Joseph I of Spain in the Peninsula war; the Spanish Constitution of 1812 was proclaimed there. Cádiz is also famous by its carnival with Chirigotas (amateur satirical choruses) competing for a prize.

Since the 1950s, a power line crosses the bay of Cádiz. The pylons on which they are mounted are from unique design.