Elena Kleshchenko's book is addressed to everyone who is interested in the practical application of genetic achievements in such areas as criminology, genealogy, and history. We are talking about the possibility of identifying a person by his genetic material. The author talks about DNA research methods and those who were at their origins: Sir Alec Jeffries, who invented DNA fingerprinting; the eccentric Kary Mullis, who managed to multiply a single DNA molecule to noticeable quantities, and other heroes of “scientific detective stories.” The detective line continues with a story about the search for criminals using DNA analysis - from Jack the Ripper to modern maniacs and terrorists. No less fascinating are historical investigations: who was Rurik - a Slav or a Scandinavian, how many descendants did Genghis Khan leave, whether the Duke of Monmouth was the son of the king of England. Why are experts confident in the accuracy of identification of the remains of Nicholas II and his family (and why do non-specialists doubt it)? In conclusion, the reader will learn why it is impossible to invent biological weapons against a certain ethnic group, whether it is possible to reconstruct one’s appearance using DNA, and whether it is dangerous to post one’s genome on the Internet.