Crop circles are areas of a grain or similar crop that have been systematically flattened to form various geometric patterns that began appearing in England in the late 1970s. One theory is that crop circles are created by flying saucers landing in a farmer's field and flattening a neat circle of the crop—however the increasing complexity of formations makes this theory less likely. Others hypothesise that these formations are sniggles or hoaxes engineered by humans. While some farmers view them as vandalism others gain revenue from charging viewers. People who study crop circle phenomenon call themselves "cerealogists". Many crop circles have fine intricate detail, regular symmetry and careful composition.
Early examples of this phenomenon were usually simple circular patterns of various sizes, which led some people to speculate that it was a natural phenomenon, but in recent years complex geometric patterns have emerged. A popular explanation is that they are either formed by extraterrestrial spaceship landings themselves or by spaceships hovering over the field to form complex patterns that contain codified messages. Other ideas on their formation have been proposed include; tornadoes, freak wind patterns, ball lightning, and something called "plasma vortices".
In the summer of 2002 Signs, a movie about crop circles which was directed by M. Night Shyamalan (the author and director of Sixth Sense) was released and attributes sinister motives to extra terrestrials in forming the circles.
Many scientists are skeptical of all the above ideas and prefer to follow the precept of Occam's Razor which would favor a mundane explanation; namely human activity. However a number of witnesses have claimed to have observed circles being created saying that it takes a few seconds and the corn falls flat like a fan being opened. Cerealogists go on to state that there are other features of crop circles that undercut the hoax theory. They say that bends in the corn in many circles are just below a joint, however they state that flattening produces a crack at any point in the stem. Also the flattened corn often lies in groomed layers, rather than random crushings.
Not long after WWII, aerial archaeological surveys were made over large areas of Britain. They photographed ripening crops to reveal crop marks, the differential ripening of the crop revealing differences in the subsoil caused by the buried remnants of ancient buildings. Though many previously unsuspected archaeological sites were found, no crop circles were ever recorded, which would tend to cast doubt on the natural forces hypothesis—unless some temporal change has happened as is seen with volcanoes and ice ages.
A decade after the phenomena began, two men announced that many crop circles were a hoax of their doing. Doug Bower and Dave Chorley argued that they had been making crop circles since 1978 using planks, rope, hats and wire as their only tools. Doug and Dave stated to reporters that a small group of people can stomp down a sizeable area of crop in a single night. Note that "stomp" does not mean using the feet. Simple tools to make crop circles have been described. 
Many subsequent crop circle makers have claimed that making what self-appointed cerealogist experts state are "unfakeable" crop circles is easy. One such cerealogist, G. Terence Meaden, was filmed claiming that a crop circle was genuine when the night before the making of that crop circle by humans was filmed. On the night of July 11-12, 1992, a crop-circle making competition, for a prize of several thousand pounds (partly funded by the Arthur Koestler Foundation), was held in Berkshire. The winning entry was produced by three helicopter engineers, using rope, PVC pipe, a trestle and a ladder. Another competitor used a small garden roller, a plank and some rope. The size and complexity of the designs produced demonstrated the minimal equipment and preparation required to produce a crop design.
Scientific American published an article by Matt Ridley (August 2002, p. 25), who started making crop circles in Texas in 1991. He wrote about how easy it is to develop techniques using simple tools that can easily fool (later) observers. He reported on "expert" sources such the Wall Street Journal who had been easily fooled, and mused about why people want to believe supernatural explanations for phenomena that are not yet explained.
Methods to create a hoaxed crop circles have been well-documented on the Internet. A counter argument to hoaxing is that circles often appears in crops mature-enough that they carry seeds, seed-pods are unbroken, whereas trampling causes seed-pod breakage. Crop circle hoaxers counter that it is easy to leave dry seed pods unbroken during stomping and also leave no trace of entrance and egress trampling when the plants and ground are both dry and some care is taken while walking. Several crop circles that were later to have been determined to be hoaxes were at first certified as being genuine by cerealogists due the lack of seed pod breakage.
Farmers are not very happy with crop circles, as they prevent the harvest of grain that has been flattened. Occasionally, perpetrators have damaged fences or other parts of farms on which they have trespassed. However people who visit the circles claim enchantment, healing and a variety of phenomena, so whether these events are wonderful or terrible depends on particular points of view.