The article deals with the problem of the interpretation of ethnogenetic legends. On the example of the legend of Czech, Lech and Rus, the legendary ancestors of the Czech, Polish and Ruthenian (Russian) peoples, the author shows that the ethnogenetic legends of the Middle Ages and early Modern Time consisted of elements of social, local, and bookish knowledge. While “social knowledge” determined basic ways of interpreting social reality, “bookish knowledge” made it possible to historize ethnogenetic legends by integrating them into a global historical narrative, and “local knowledge” is used for linking the ethnogenetic construction to a particular cultural landscape. Taking into account the discursive character of the very concept of “ethnogenesis”, the author considers the interaction of elements of “social”, “local” and “bookish” knowledge as a universal model for the formation of not only pre-modern but also modern ethnogenetic constructions.