The problem of reception of the concept “res publica” is complex and multifaceted. It has been thoroughly studied in relation to the period of the Middle Ages. The task of the author is to demonstrate, that the possibilities of applying the information approach to the field of cognitive surveying to reveal the content of receptions and LatinGreek transliterations of the concept “res publica” with the help of the Expert System “Byzantine Law and Acts”. The comparisons of Greek translations and compilations with their Latin prototypes of Byzantine law prove: their compilations did not necessarily follow their prototypes in conveying the notion of “res publica”. It, as a rule, was replaced by other Greek concepts and word-combinations. For them, as well as their Latin prototypes, a certain semantic ambiguity is evident. Accordingly, the mediaeval Byzantine jurists felt the need to use the direct reception of the Latin concept “res publica”, in particular “rei publicae causa”. It served as the subject of attention and professional lawyers used this concept to interpret and explain the content of the sources of medieval Byzantine law. Noticeable discrepancies in the recording forms of the identified receptions and Greek transliterations of the concept “res publica” are probably due to individual characteristics of Medieval Byzantine lawyers and their professional qualifications. The direct borrowings of the concept “res publica causa” or its transliterations, revealed in medieval Byzantine law monuments, were purely terminological in most cases. It, if it is admissible, may be considered as a kind of cultural phenomenon.