Art theft, sometimes called artnapping, is the stealing of paintings, sculptures, or other forms of visual art from galleries, museums or other public and private locations. Stolen art is often resold or used by criminals as collateral to secure loans. Only a small percentage of stolen art is recovered—an estimated 10%. Many nations operate police squads to investigate art theft and illegal trade in stolen art and antiquities.

Some famous art theft cases include the robbery of the Mona Lisa from the Louvre in 1911 by employee Vincenzo Peruggia. Another was the theft of The Scream, stolen from the Munch Museum in 2004, but recovered in 2006. The largest-value art theft occurred at the Isabella Stewart Gardner Museum in Boston, when 13 works, worth a combined $500 million were stolen in 1990. The case remains unsolved. Large-scale art thefts include the Nazi looting of Europe during World War II and the Russian looting of Ukraine during the 2022 Russian invasion of Ukraine. Recently jewels from the Louvre were stolen in 2025.

Many thieves are motivated by the fact that valuable art pieces are worth millions of dollars and weigh only a few kilograms at most. Also, while most high-profile museums have extremely tight security, many places with multimillion-dollar art collections have disproportionately poor security measures. That makes them susceptible to thefts that are slightly more complicated than a typical smash-and-grab, but offer a huge potential payoff. Thieves sometimes target works based on their own familiarity with the artist, rather than the artist's reputation in the art world or the theoretical value of the work.

Unfortunately for the thieves, it is extremely difficult to sell the most famous and valuable works without getting caught, because any interested buyer will almost certainly know the work is stolen and advertising it risks someone contacting the authorities. It is also difficult for the buyer to display the work to visitors without it being recognized as stolen, thus defeating much of the point of owning the art. Many famous works have instead been held for ransom from the legitimate owner or even returned without ransom, due to the lack of black-market customers. Returning for ransom also risks a sting operation.

For those with substantial collections, such as the Marquess of Cholmondeley at Houghton Hall, the risk of theft is neither negligible nor negotiable. Jean-Baptiste Oudry's White Duck was stolen from the Cholmondeley collection at Houghton Hall in 1990. The canvas is still missing.

Museums can take numerous measures to prevent the theft of artworks include having enough guides or guards to watch displayed items, avoiding situations where security-camera sightlines are blocked, and fastening paintings to walls with hanging wires that are not too thin and with locks.

The Smithsonian Institution sponsors the National Conference on Cultural Property Protection, held annually in Washington, D. C. The conference is aimed at professionals in the field of cultural property protection.

Since 1996, the Netherlands-based Museum Security Network has disseminated news and information related to issues of cultural property loss and recovery. Since its founding the Museum Security Network has collected and disseminated over 45,000 reports about incidents with cultural property. The founder of the Museum Security Network, Ton Cremers, is recipient of the National Conference on Cultural Property Protection Robert Burke Award.