What do we know about secret societies? These are organizations that for some reason hide their activities, and sometimes their very existence. They are characterized by special rituals related to their initiation and inner life, as well as special signs that distinguish its participants. Secret societies can be religious, political or social. But the main question is: what is all this secrecy for? The famous Russian researcher of catacombs and dungeons, the author of the bestseller "Legends of the Moscow Metro" Matvey Grechko is trying to answer this question in his book "Secret Societies. Full story." He identifies several criteria by which certain associations hide their activities, and examines them in detail on the example of specific organizations: from secret societies of the ancient world with their mysteries, early Christian communities, medieval Cathars, Templars, alchemists and Rosicrucians to modern associations, including Freemasons and related orders. The author also pays attention to revolutionary societies, Russian heretical sects, criminal, occult, Nazi and many other secret organizations.