A crop circle is a sizable pattern created by the flattening of a crop such as wheat, barley, rye, maize, or rapeseed. Crop circles are also referred to as crop formations, because they are not always circular in shape. While the exact date crop circles began to appear is unknown, the documented cases have substantially increased from the 1970s to current times. Twenty-six countries ended up reporting approximately ten thousand crop circles, in the last third of the 20th century, and 90% of those were located in southern England. Many of the formations appearing in that area are positioned near ancient monuments, such as Stonehenge. According to one study, nearly half of all circles found in the UK in 2003 were located within a 15 km (9.3 miles) radius of Avebury.

A couple of articles dealing with the analysis of samples taken from crop circles.

Small publisher of crop circles books by Andy Thomas, including the guidebook Vital Signs.

Information about a graphic novel that will incorporate the crop circle phenomenon.

Provides views of each crop circles at ground level, using photographs, first hand reports and observations.

There is a divine intelligence in the DNA, what the Hindus call the Inner Self, that is responsible for creating crop circles.

Information about crop formations and images.

The Mythologist is a film about crop circle / ufo researcher Armen Victorian aka Henry Azadehdel.

Site trying to test if researchers are able to distinguish between genuine and man-made crop circles.

Web site of crop circle photographer Steve Alexander and writer Karen Douglas. Online image library, online shop of stock photos and a selection of articles.

A rolling news service for the crop circle phenomenon.

Report from the America Institute of Physics about the diatonic ratios found in crop circles.

In 1992, PSI TECH was hired to examine function/purpose, and mechanics of the Crop circle production.

A feature-length documentary full of never-before-seen footage and interviews with leading Crop Circle researchers and scientists.

A guide to all those things, from aliens to crop circles, from spontaneous human combustion to disappearances, from ghosts to ley lines.

The first place to look for all the information on Oxfordshire crop formations.

Games and books created by mystic merlin.

Crop circles related art work.

Leading annual conference on crop formations and related issues, in Glastonbury, SW England, July/August.

Crop circles from Germany. Most articles have an English translation.

Reports and articles about Dutch crop circles.

Complete archive of formations dating back to 1590. Articles and other resources. Both Dutch and English.

An introduction to the subject with images and links to latest developments.