Helen of Troy, Helen, Helena, (Ancient Greek: Ἑλένη, romanized: Helénē, pronounced [helénɛː]) also known as beautiful Helen, Helen of Argos, or Helen of Sparta, was a figure in Greek mythology said to have been the most beautiful woman in the world. She was believed to have been the daughter of Zeus and Leda, and was the sister of Clytemnestra, Castor and Pollux, Philonoe, Phoebe and Timandra. She was married to King Menelaus of Sparta "who became by her the father of Hermione, and, according to others, of Nicostratus also." Her abduction by Paris of Troy was the most immediate cause of the Trojan War.

Elements of her putative biography come from classical authors such as Aristophanes, Cicero, Euripides, and Homer (in both the Iliad and the Odyssey). Her story reappears in Book II of Virgil's Aeneid. In her youth, she was abducted by Theseus. A competition between her suitors for her hand in marriage saw Menelaus emerge victorious. All of her suitors were required to swear an oath (known as the Oath of Tyndareus) promising to provide military assistance to the winning suitor, if Helen were ever stolen from him. The obligations of the oath precipitated the Trojan War. When she married Menelaus she was still very young; whether her subsequent departure with Paris was an abduction or an elopement is ambiguous (probably deliberately so).

The legends of Helen during her time in Troy are contradictory: Homer depicts her ambivalently, both regretful of her choice and sly in her attempts to redeem her public image. Other accounts have a treacherous Helen who simulated Bacchic rites and rejoiced in the carnage she caused. In some versions, Helen doesn't arrive in Troy, but instead waits out the war in Egypt. Ultimately, Paris was killed in action, and in Homer's account Helen was reunited with Menelaus, though other versions of the legend recount her ascending to Olympus instead. A cult associated with her developed in Hellenistic Laconia, both at Sparta and elsewhere; at Therapne she shared a shrine with Menelaus. She was also worshiped in Attica and on Rhodes.

Her beauty inspired artists of all times to represent her, frequently as the personification of ideal human beauty. Images of Helen start appearing in the 7th century BC. In classical Greece, her abduction by Paris—or escape with him—was a popular motif. In medieval illustrations, this event was frequently portrayed as a seduction, whereas in Renaissance paintings it was usually depicted as a "rape" (i. e. abduction) by Paris. Christopher Marlowe's lines from his tragedy Doctor Faustus (1604) are frequently cited: "Was this the face that launched a thousand ships / And burnt the topless towers of Ilium?"