Dénia, also known as Denia, is a historical coastal city and municipality in the province of Alicante, Spain, on the Costa Blanca halfway between Alicante and Valencia, and the capital and judicial seat of the comarca of Marina Alta. Denia's historical heritage has been influenced by Iberian, Greek, Roman, Islamic, Napoleonic and Christian civilizations. As of 2024^[update], it had a population of 49,700, although this is more than doubled by tourism during the summer months.

There is evidence of human habitation in the area since prehistoric times and there are significant Iberian ruins on the hillsides nearby. In the 4th century BC it was a Greek colony of Massalia or Emporion,^{[citation needed]} perhaps the one mentioned by Strabo as Hēmeroskopeion (Ancient Greek: Ἡμεροσκοπεῖον) (meaning "watchtower"). It was an ally of Rome during the Punic Wars, and later was absorbed into the Roman Empire under the name of Dianium (after their goddess Diana). In the 1st century BC Quintus Sertorius established a Roman naval base here.

From 636–696, under Visigothic rule, it was the seat of a bishop subordinate to Toledo. After the Muslim conquest of Iberia and the dissolution of the Caliphate of Córdoba, Dénia (Arabic: دانية, Dāniyya) became the capital of a Taifa kingdom that reigned over part of the Valencian coast and Ibiza. Slavic Muslim slaves, saqālibah, led by Mujahid ibn Yusuf ibn Ali, profited from the progressive crumbling of the Caliphate's superstructure to gain control over the province of Dénia. The saqālibah managed to free themselves and run the kingdom, which extended its reach as far as the islands of Mallorca and its capital Madinah Mayurqah [es]. The saqālibah taifa lost its independence in 1076, when it was captured by Ahmad al-Muqtadir, lord of Zaragoza, under which it remained until the Almoravid invasion in 1091. The Muslim Arabs originally built the castle fortress, and the French, who occupied the city for four years during the Peninsular War, rebuilt it in the early 19th century.

The town was conquered by the Christians in 1244. This caused a decline for the city, which remained nearly uninhabited after the exile of most of the Muslim population. It was later repopulated by the Valencian government. Created a fief in 1298, it was held by the de Sandoval family from 1431, although the city itself was returned to the Aragonese crown in 1455. A marquisate from 1487, Dénia gained many privileges thanks to Francisco Gómez de Sandoval y Rojas, Duke of Lerma, a favourite of Philip III of Spain. It suffered a further period of decay after the decree of Expulsion of the Moriscos (1609), by which 25,000 people left the marquisate, leaving the local economy in a dismal state.

During the War of the Spanish Succession Dénia was besieged by 9,000 French troops in June 1707, who broke down several sections of the town walls using cannon, but their attacks in July were repulsed by the small garrison with great loss of life to the attackers resulting in the siege being raised after 27 days. Dénia, however, fell to the French forces that November. In 1713 the Treaty of Utrecht recognised Louis XIV's grandson Philip, Duke of Anjou, as King of Spain (as Philip V), so returning Dénia to Spanish rule.

It was reacquired by the Spanish crown in 1803, after which Denia gained an increasingly important role as a trading port. A community of English raisin traders lived in Denia from 1800 until the time of the Spanish Civil War in the late 1930s.

Dénia is home to a large Moorish castle named Castle of Dénia on a rocky crag overlooking the city. It was built in the 11th and 12th century and offers views around the sea, the city and the surrounding area. Located in the castle is the Palau del Governador and its corresponding museum.

Dénia also has the Museu Etnològic with further details on the history and culture of the city.