An out-of-place artifact, or OOPArt, is an object that interests people studying history, archaeology, or ancient life. It is said to have been found in a place or time that challenges what scientists normally believe about when certain events or technologies occurred. Some people believe these artifacts are too advanced for the time they were found, or that humans existed earlier than history suggests. Others think they show that different cultures interacted in ways that are hard to explain with regular history.

This idea is used in areas of study that are not widely accepted, such as cryptozoology, ancient astronaut theories, young Earth creationism, and paranormal research. It can describe many types of items, from objects studied by scientists to those linked to fake stories or explained by regular science.

Critics say that most OOPArts that are not hoaxes are the result of misunderstandings or wishful thinking. For example, someone might think a culture couldn’t have made a certain object because they didn’t have the right tools or materials. Sometimes, confusion comes from incorrect descriptions. The Wolfsegg Iron is not a perfect cube, and the Klerksdorp spheres are not perfect spheres. The Delhi Iron Pillar was said to not rust, but it has some rust near its bottom. Its resistance to rust is because of materials used during its creation and environmental conditions.

Some people believe OOPArts show that mainstream science is missing important knowledge, either on purpose or by accident. Many researchers who question traditional ideas about history use OOPArts to support their arguments. Creation science often uses these objects to challenge scientific ideas about human history and evolution. Some people use OOPArts to support religious views of the past, ancient astronaut theories, or the idea that ancient civilizations had advanced knowledge. Supporters also suggest there is an "alternative history," and books about this are popular among people who believe in hidden truths.