Éowyn (/ˈeɪoʊwɪn/ or /ˈeɪoʊwuːn/) is a fictional character in J. R. R. Tolkien's The Lord of the Rings. She is a noblewoman of Rohan who describes herself as a shieldmaiden.

With the hobbit Merry Brandybuck, she rides into battle and kills the Witch-King of Angmar, Lord of the Nazgûl, in the Battle of the Pelennor Fields. This fulfils the Macbeth-like prophecy that he would not be killed by a man.

Éowyn's brief courtship by Faramir has been seen by scholars as influenced by Tolkien's experience of war brides from the First World War. She has been seen, too, as one of the few strong female characters in the story, especially as interpreted in Peter Jackson's film trilogy, where her role, played by Miranda Otto, is far more romantic than Tolkien made her.

In The Two Towers, Éowyn, a daughter of the House of Eorl and the niece of King Théoden of Rohan, is introduced in Meduseld, the King's hall at Edoras. She is the daughter of Éomund and Théodwyn (Théoden's sister), and the sister of Éomer. When she is only seven years old, her father is killed fighting orcs, and her mother dies of grief. Éowyn and Éomer are raised in her uncle's household as his own children.

She longs to win renown in battle—especially since she is royal—but being female, her duties are reckoned to be at Edoras. When Théoden's mind is poisoned by his corrupt adviser Gríma Wormtongue, Éowyn is obliged to care for her uncle, and his deterioration pains her deeply. To make matters worse, she is constantly harassed by Gríma, who lusts after her. When Gandalf arrives, he frees Théoden from Wormtongue's influence. Éowyn falls in love with Aragorn, but though he respects her, he does not return her feelings, as he is betrothed to the elf Arwen. As Aragorn points out, her duty is with her people; she has to shoulder the responsibility of ruling Rohan in Théoden's stead when the war-host of Rohan go to war.

I am weary of skulking in halls, and wish to face peril and battle. … am I not of the House of Eorl, a shieldmaiden … may I not now spend my life as I will? … All your words are but to say: you are a woman and your part is in the house. But when the men have died in battle and honour, you have leave to be burned in the house, for the men will need it no more. But I am of the House of Eorl and not a serving-woman. I can ride and wield blade, and I do not fear either pain or death. …[I fear] A cage, To stay behind bars, until use and old age accept them, and all chance of doing great deeds is gone beyond recall or desire.

Éowyn disguises herself as a man and, under the alias of Dernhelm (from Old English dern meaning "secret, concealed"), travels with the Riders of Rohan to the battle outside Minas Tirith in Gondor on her horse Windfola, carrying with her the hobbit Merry Brandybuck, who had also been ordered to remain behind.

In the Battle of the Pelennor Fields, she confronts the Witch-King of Angmar, Lord of the Nazgûl, after Théoden is mortally injured. The Witch-King threatens that he will "bear thee away to the houses of lamentation, beyond all darkness, where thy flesh shall be devoured, and thy shrivelled mind be left naked to the Lidless Eye". He boasts "No living man may hinder me", whereupon Éowyn removes her helmet and declares: