Crop circles, also known as crop formations, are patterns made by flattening crops, a phenomenon that gained prominence in the early 1980s. While fringe theories suggest natural or extraterrestrial origins, all documented cases are consistent with human creation. In 1991, Doug Bower and Dave Chorley claimed responsibility for starting the trend in England in 1978, stating they created over 200 circles. Their confessions, and the subsequent media attention, led to a significant increase in reported crop circles worldwide.

Reports indicate that crop circles in the UK are not randomly distributed but tend to appear near populated areas, roads, and historical monuments, often overnight. This pattern, along with their increasing complexity and size, suggests intentional human activity rather than paranormal causes. The phenomenon has also spurred tourism and commercial ventures, with art collectives and businesses creating crop circles for artistic and commercial purposes.

While the term "crop circle" emerged in the early 1980s, historical accounts of unusual crop patterns date back centuries. A 1678 pamphlet described a "Mowing-Devil" cutting crops, and in 1686, naturalist Robert Plot noted rings of mushrooms, suggesting aerial influences. In 1880, amateur scientist John Rand Capron reported circles of flattened crops, speculating about "cyclonic wind action." In the 20th century, observations included archaeological cropmarks, and reports of flattened areas in fields, sometimes with spiral patterns, were attributed to various causes including meteoric impacts or lightning strikes. The 1960s saw numerous UFO sightings and circular formations in Australia and Canada, with some investigations concluding artificial origins, though natural causes like downdrafts were also proposed.

The modern phenomenon of geometric crop circles appears to have been significantly influenced by the 1966 Tully "saucer nest" incident in Australia and the 1974 science-fiction film "Phase IV." British pranksters Doug Bower and Dave Chorley claimed to have started creating crop circles in 1978, inspired by these events. They used simple tools like planks and ropes to create patterns, eventually taking credit for over 200 circles. Their confessions in 1991, coupled with media coverage, led to a global surge in crop circle reports. Researchers noted that these formations often appeared in accessible locations near populated areas and cultural landmarks, strengthening the argument for human causation. The phenomenon also generated considerable public interest, leading to tourism and commercial opportunities.

Since the late 1970s, crop circles have evolved significantly in complexity and design. By the 21st century, formations featured intricate geometric patterns, sometimes incorporating advanced mathematical and scientific concepts. This evolution has been driven by anonymous artists and collectives, such as the UK arts collective Circlemakers, founded in the early 1990s. These groups have created crop circles both as an art practice and for commercial clients, demonstrating a clear human agency behind the phenomenon. The appearance of crop circles has also been linked to media attention and the absence of restrictive legislation, further facilitating their creation and dissemination across the globe.