Leonardo da Vinci's Mona Lisa painting, in the Louvre in Paris, is arguably the most famous painting in the world. It is probably also the best known example of sfumato, a painting technique partly responsible for her enigmatic smile.
There's been a lot of speculation about who the woman in the painting was. It's thought to be a portrait of Lisa Gherardini, wife of a Florentine cloth merchant called Francesco del Giocondo.