The document provides an overview of the history and evidence surrounding crop circles. It discusses early historical accounts of crop circles from the 17th century. It then covers the proliferation of crop circles starting in the 1970s and analyses various characteristics of crop circles like plant effects, soil effects, and electromagnetic field anomalies found at crop circle sites. The document also discusses both theories for the circles being caused by natural or man-made causes as well as the possibility of them being created by extraterrestrial phenomena.