This publication is devoted to legal fiction, one of the most sought-after instruments of jurisprudence in ancient Rome, and offers an explanation of its popularity among ancient lawyers by the specifics of their ideas about the place of law in the system of social regulation, about its relationship with social reality. The book examines many specific cases of the use of fiction (in the institutions of adoption, guardianship, to formalize the invalidity of transactions), and also analyzes the judgments of the Romans themselves about fiction and their general legal views, which caused such a bizarre use of legal technology.