La Belle Ferronnière (French pronunciation: [la bɛl fɛʁɔnjɛʁ]) is a portrait of a lady, usually attributed to Leonardo da Vinci, in the Louvre. It is also known as Portrait of an Unknown Woman. The painting's title, applied as early as the seventeenth century, identifying the sitter as the wife or daughter of an ironmonger (a ferronnier), was said to be discreetly alluding to a reputed mistress of Francis I of France, married to a certain Le Ferron. Later she was identified as Lucretia Crivelli, a married lady-in-waiting to Duchess Beatrice of Milan, who became another of the Duke's mistresses.

Leonardo's Lady with an Ermine has also been known by this name. This was once believed to be a portrait of Cecilia Gallerani, one of the mistresses of Ludovico Sforza, Duke of Milan.[2] The narrative and the title were applied to Lady with an Ermine when it was in Princess Izabela Czartoryska's collection, and became confused with La Belle Ferronnière by the presence of a ferronnière, a type of accessory worn across the forehead, in the painting as well.