Everyone knows the Mona Lisa. It is, perhaps, the most iconic piece of art in the world. But why is it so famous? If you are like many people, you will begin your search for an explanation of the painting’s fame by recalling what you know about good art and about the Mona Lisa. Good art is masterful, and Leonardo da Vinci is a master. Good art fascinates and challenges us, and the Mona Lisa’s expression is a puzzle for us to unlock.