The "Mona Lisa" was stolen by an employee of the Louvre.

Some people just can't keep their hands off other people's things -- even the world's greatest art. Art thieves take their loot from museums, places of worship, and private residences. Because they would have trouble selling the fruits of their labor on the open market -- auction houses and galleries tend to avoid stolen works -- art burglars often either keep the art for themselves or try to ransom the hot property back to the original owner. Among the major robberies in the past hundred years are these daring thefts of very expensive art (values estimated at the time of the theft).

1. Boston, March 1990: $300 million

Two men dressed as police officers visited the Isabella Stewart Gardner Museum in the wee hours of the morning. After overpowering two guards and grabbing the security system's surveillance tape, they collected Rembrandt's only seascape, "Storm on the Sea of Galilee," as well as Vermeer's "The Concert, Manet's Chez Tortoni," and several other works. Authorities have yet to find the criminals despite investigating everyone from the Irish Republican Army to a Boston mob boss!

2. Oslo, August 2004: $120 million

Two armed and masked thieves threatened workers at the Munch Museum during a daring daylight theft. They stole a pair of Edvard Munch paintings, "The Scream" and "The Madonna," estimated at a combined value of 100 million euros. In May 2006, authorities convicted three men who received between four and eight years in jail. The paintings were recovered three months later.

3. Paris, August 1911: $100 million

In the world's most notorious art theft to date, Vincenzo Peruggia, an employee of the Louvre, stole Leonardo da Vinci's "Mona Lisa" from the storied museum in the heart of Paris. Peruggia simply hid in a closet, grabbed the painting once alone in the room, hid it under his long smock, and walked out of the famed museum after it had closed. The theft turned the moderately popular "Mona Lisa" into the best-known painting in the world. Police questioned Pablo Picasso and French poet Guillaume Apollinaire about the crime, but they found the real thief -- and the Mona Lisa -- two years later when Peruggia tried to sell it to an art dealer in Florence.

Read about more outrageous art thefts on the next page.