Atlantis is an ancient island that sunk into the ocean, according to the Classical Greek philosopher Plato, who tells the story in his dialogues. While most people today believe that the story of Atlantis is simply allegory, the idea of a lost continent has captured public imagination since the days of Plato. Atlantis was supposedly home to an advanced civilization that had conquered many nations before failing in combat against Athens and collapsing into the ocean during an earthquake.

It is a matter of speculation whether or not the idea of Atlantis or a similar island predates Plato, as no earlier ancient sources are known. In the Classical era, philosophers and historians were divided over whether or not the story of Atlantis had any basis in fact. Though some claimed to have proof of the island's existence, none of it was definitive. Some writers of the ancient era wrote their own stories of vanished utopias that appear to parody Plato's Atlantis.

In the Middle Ages, the story of Atlantis was largely forgotten, but it resurfaced during the Enlightenment, when Francis Bacon used it as a symbol of Utopia in his The New Atlantis (1626). Bacon's account of Atlantis is similar to that of Plato, except that Bacon places the island in the Americas. In the late 19th century, the idea of a historical Atlantis regained popularity, and many expeditions sought proof of its existence. Scholars theorized a link between Atlantis and Mesoamerican cultures such as the Aztecs. Atlantis was often portrayed as a very advanced society, with technology surpassing that of the present, and it began to interest those in Spiritualist circles.

Though Plato portrayed Atlantis as a flawed society, the antithesis to the ideal of Athens, the missing island became increasingly interpreted as a pinnacle of culture and enlightenment in the modern era. While the current understanding of plate tectonics has made the possibility of a real Atlantis unlikely to say the least, the vanished continent remains a powerful cultural symbol. Atlantis often appears in science fiction and fantasy works of all kinds, from books and films to video games and cartoons.