What is a UFO? Alien ships with mysterious aliens? Or maybe this is another form of life that exists on Earth in a dimension invisible to us? Are these mysterious phenomena mentioned in the Bible and other ancient sources? The book examines the history of human contacts with unidentified flying objects throughout the millennia-long history of civilizations - from ancient times to the present day. Evidence of recent meetings of people with messengers of the “invisible world”, the opinions of scientists and researchers of the unknown are given. The picture is complemented by declassified information from the archives of the military departments of a number of countries.