Crop circles are large patterns that appear in fields of wheat, rye, barley and similar crops. The patterns can be intricate geometric, circular or abstract and are usually formed when the stems of the crop are broken at ground level or at node points and flattened to the ground in the same direction.

While some crop circles can be explained, others remain a mystery. The crop circles that cannot be proven to be man-made often exhibit peculiar characteristics that are difficult or impossible to duplicate.