The present thesis investigates why some homographic words of the closely related Slavic languages Russian and Bosnian/Croatian/Serbian have entirely different meanings. These words are often colloquially referred to as „false friends“, whereas in the (Slavic) linguistic literature, they are known as „interlingual homonyms“. It is the aim of this study to explore various possible reasons for the emergence of homonymy from a diachronic perspective. For this purpose, a corpus of 140 interlingual homonyms (consisting of both nouns and adjectives) was assembled and examined by means of etymological dictionaries. Genetically related Slavic words made up the greatest part of analysed examples, which is why the process of semantic divergence appeared to be the most frequent reason for interlingual homonymy. Furthermore, individually modified loanwords as well as the graphical convergence of etymologically different words in Russian and Bosnian/Croatian/Serbian were the causes of homonymy in about one third of the examined cases.