Five centuries after Leonardo da Vinci painted the Mona Lisa (1503–19), the portrait hangs behind bulletproof glass within the Louvre Museum and draws thousands of jostling spectators each day. It is the most famous painting in the world, and yet, when viewers manage to see the artwork up close, they are likely to be baffled by the small subdued portrait of an ordinary woman. She’s dressed modestly in a translucent veil, dark robes, and no jewelry. Much has been said about her smile and gaze, but viewers still might wonder what all the fuss is about. Along with the mysteries of the sitter’s identity and her enigmatic look, the reason for the work’s popularity is one of its many conundrums. Although many theories have attempted to pinpoint one reason for the art piece’s celebrity, the most compelling arguments insist that there is no one explanation. The Mona Lisa’s fame is the result of many chance circumstances combined with the painting’s inherent appeal.

There is no doubt that the Mona Lisa is a very good painting. It was highly regarded even as Leonardo worked on it, and his contemporaries copied the then novel three-quarter pose. The writer Giorgio Vasari later extolled Leonardo’s ability to closely imitate nature. Indeed, the Mona Lisa is a very realistic portrait. The subject’s softly sculptural face shows Leonardo’s skillful handling of sfumato, an artistic technique that uses subtle gradations of light and shadow to model form, and shows his understanding of the skull beneath the skin. The delicately painted veil, the finely wrought tresses, and the careful rendering of folded fabric reveal Leonardo’s studied observations and inexhaustible patience. And, although the sitter’s steady gaze and restrained smile were not regarded as mysterious until the 19th century, viewers today can appreciate her equivocal expression. Leonardo painted a complex figure that is very much like a complicated human.