The best-known, most visited, most written-about portrait in the world is a painting of a smiling woman by Leonardo da Vinci.
It is an oil painting on a poplar wood panel. Most experts believe it is a picture of Lisa Gherardini, a woman who lived in Italy in the 1500s. Almost nothing else is known about her or her famous smile.
The Mona Lisa has been on permanent display in the Louvre Museum in Paris since 1797.
The directors of the Louvre have been covering up a secret for several years: someone stole the Mona Lisa.
Visitors who go to the famous museum to view the portrait are now staring at page 967 of Famous Art You Should Know from Around the World.
No one has any idea where the real painting is, or how thieves were able to break into the museum. There were no clues other than a terrible, terrible smell.
French authorities, art experts, and customs agents have been searching the globe for the original masterpiece for many years.
Every museum guard in the world secretly hopes to be the one who rescues the Mona Lisa.