The roughly trapezoidal island is formed by a complex volcano immediately southwest of the Campi Flegrei area at the western side of the Bay of Naples.

The eruption of the trachytic Green Tuff Ignimbrite about 56,000 years ago was followed by the formation of a caldera comprising almost the entire island and some of the surrounding seabed.

[4] The highest point of the island, Monte Epomeo (788 m (2,585 ft)), is a volcanic horst consisting of green tuff that was submerged after its eruption and then uplifted.

Volcanism on the island has been significantly affected by tectonism that formed a series of horsts and grabens; resurgent doming produced at least 800 m (2,600 ft) of uplift during the past 33,000 years.

Following the volcanic activity of Epomeo, "...the sea receded for three stages; afterwards (...) it turned back again and its ebb tide submerged the island (...) those who lived on the mainland fled from the coast into the interior of Campania" (Geography V, 4, 9).

After eruptions in Greek and Roman times, the last one occurred in 1302 in the eastern sector of the island with a brief flow (known as Arso) reaching the sea.

The first evidence of the island's current toponym dates back to the year 812, in a letter from Pope Leo III in which he informs Emperor Charlemagne of devastations that occurred in the area, calling the island Iscla maior: "Ingressi sunt ipsi nefandissimi Mauri [...] in insulam, quae dicitur Iscla maiore, non longe a Neapolitana urbe."

The Phoenician presence on the island is archaeologically documented from a very ancient era and, as reported by Moscati (an Italian historian), in the spread in Campania and southern Etruria, since the 8th century BC, of objects of Egyptian production or inspiration, "the Phoenician merchants settled in Ischia and then frequented the Tyrrhenian coasts" certainly played a part.

[13] Martianus Capella followed Virgil in this allusive name, which was never in common circulation: the Romans called it Aenaria, the Greeks, Πιθηκοῦσαι, Pithekoūsai.

However, Pliny derives the Greek name from the local clay deposits, not from píthēkos; he explains the Latin name Aenaria as connected to a landing by Aeneas (Princeton Encyclopedia).

If the island actually was, like Gibraltar, home to a population of monkeys, they were already extinct by historical times as no record of them is mentioned in ancient sources.

Euboean Greeks from Eretria and Chalcis arrived in the 8th century BC to establish an emporium for trade with the Etruscans of the mainland.

In 474 BC, Hiero I of Syracuse came to the aid of the Cumaeans, who lived on the mainland opposite Ischia, against the Etruscans and defeated them on the sea.

In 1422 Joan II gave the island to her adoptive son Alfonso V of Aragon, though, when he fell into disgrace, she retook it with the help of Genoa in 1424.

In 1438 Alfonso reoccupied the castle, kicking out all the men and proclaiming it an Aragonese colony, marrying to his garrison the wives and daughters of the expelled.

Ferdinand I of Naples ordered Alessandro Sforza to chase Torella out of the castle and gave the island over, in 1462, to Garceraldo Requesens.

In February 1495, with the arrival of Charles VIII, Ferdinand II landed on the island and took possession of the castle, and, after having killed the disloyal castellan Giusto di Candida with his own hands, left the island under the control of Innico d'Avalos, marquis of Pescara and Vasto, who ably defended the place from the French flotilla.

With the increasing rarity and diminishing severity of the piratical attacks later in the century and the construction of better defences, the islanders began to venture out of the castle and it was then that the historic centre of the town of Ischia was begun.

The island participated in the short-lived Republic of Naples starting in March 1799 but by April 3 Commodore Thomas Troubridge under the command of Lord Nelson had put down the revolt on Ischia as well as on neighboring Procida.

Rudolf Levy, Werner Gilles, Max Peiffer Watenphul with Kurt Craemer and Vincent Weber stayed in the fishing village of Sant'Angelo on the southern tip of the island shortly before the outbreak of the Second World War.

From Ischia, various destinations such as Naples, Vesuvius, Amalfi Coast, Capri, Herculaneum, Paestum and the neighboring island Procida can be booked.

The island is home to the Ischia Film Festival, an international cinema competition celebrated in June or July, dedicated to all the works that have promoted the value of the local territory.

Vineyards planted within the 179 hectares (440 acres) boundaries of the DOC tend to be on volcanic soils with high pumice, phosphorus and potassium content.

[30] The white wines of the island are composed primarily of Forastera (at least 65% according to DOC regulation) and Biancolella (up to 20%) with up to 15% of other local grape varieties such as Arilla and San Lunardo.

Only certain subareas of the Ischia DOC can produce Bianco Superiore with the blend needing to contain 50% Forastera, 40% Biancolella and 10% San Lunardo.

Like the white wines, red grapes destined for DOC production are limited to a harvest yield of no more than 10 tonnes/ha though the minimum finished alcohol level is higher at 11.5% ABV.

Around 1700, about 2000 families lived on the islet, including a Poor Clares convent, an abbey of Basilian monks (of the Greek Orthodox Church), the bishop and the seminar, and the prince, with a military garrison.

Surrounded by a park, the villa (called "The Dovecote") was made by Luigi Patalano, a famous local socialist and journalist.

[citation needed] In 2004 one of the five communities of the island commenced civil works to build a sewage treatment plant but since then the construction has not been completed and it is currently stopped.

[36] The breakage of the Enel cable resulted in the spillage of oil into the sea and into other environmental matrices – with the consequent pollution by polychlorobiphenyls (PCBs, the use of which was banned by the Italian authorities as long ago as 1984), polycyclic aromatic hydrocarbons (PAHs) and linear alkyl benzenes (aromatic hydrocarbons) — in the ‘Regno di Nettuno’, a marine protected area, and the largest ecosystem in the Mediterranean Sea, designated as a ‘priority habitat’ in Annex I to the Habitats Directive (92/43/EEC) and comprising oceanic posidonia beds.