This thesis provides an insight into the position of English as the dominant lingua franca from the perspective of Croatian public figures’ use of English on Instagram. The main aim of the conducted research was to examine, detect and indicate the main problems of Croatians’ use of English on social media, in this particular case, Instagram. The first part of the thesis is the theoretical background based on definitions of English as a lingua franca, explaining the reasons which contributed to it obtaining such a position, as well as the most prominent context in which it is used. What has also been dealt with is the influence that English has had on language use in the Croatian context. This part is concluded with a brief insight into the social media platforms in general, with a special emphasis on Instagram, and the characteristics of communication commonly performed on such platforms. The second part represents the analysis of the ways in which English is used by famous Croatian Instagram users. During the analysis, two basic types of deviations were identified, those related to grammar and orthography. The analysis of the use of English by Croatian Instagram users revealed a number of different grammatical and orthographic issues.