Do aliens exist? Science, in spite of a traditionally skeptical approach, today is oriented to answer positively. In the most exhausting terms, this book travels over the several stages of this historical, cultural, scientific and spiritual question, within humankind since the antiquity and today, nowadays updated, from the one hand, by four decades of radioastronomy research on and, from the other hand, by a century of official and non official investigations on the UFO phenomenon. This book delineates moreover the scenarios that would take place in contact with alien civilizations, both in positive and negative ways: an epochal event that could disclose to us a new vision of the world. Pinotti's books are usually a good start for those wanting to read about UFOs, and this is no exception.