The late Dr. Allen J. Hynek, founding member of Centre for UFO Studies and USAF Chief Scientific Advisor from 1948 – 1969 was responsible for the development of the Close Encounters (CE) Classification.
Known throughout the world the CE Classification is widely used as a reporting reference for researchers of the UFO phenomenon. 


CE 1 (Close Encounters of the First Kind)
Where the observer or multiple observers witness an aerial object of an unknown nature.

CE 2 (Close Encounters of the Second Kind)
Physical trace left by an aerial object of an unknown nature.

CE 3 (Close Encounters of the Third Kind)
Where an observer or multiple observers claim to have witnessed occupants of a UFO (Unidentified Flying Object).

CE 4 (Close Encounters of the Fourth Kind)
Claims of an abduction by foreign intelligence (extraterrestrial).