The aim of the research in this PhD thesis is to deepen the understanding about potentials of new media in realizing foreign policy interests of the Republic of Croatia through the research and analysis of the experiences and practices of online international communications of countries with more developed diplomatic infrastructure (Western and Central European countries, "old" European Union member states) and transition countries (Middle- and Eastern European countries - "new" European Union member states, as well as selected candidate countries for membership in the European Union). The situation in Croatia was compared with the situation in the mentioned groups of countries and the main factors that have influenced and/or affected diagnosed condition of their online subsystems of international public communication have been identified. With aim to give a comprehensive view of the conditions in which public diplomacy of individual countries has developed, legal, political and social factors were analyzed in correlation with media policies and national specificities. Theoretical framework included a review of research of the subject by foreign and domestic authors, as well as legislation of the European Union and legislation of groups of countries involved in the analysis, with the necessity of defining and describing the characteristics of new media and their evolution in general terms but also in the context of their use in diplomatic practice - through the development of public diplomacy. The empirical framework included three levels of research: the analysis of online communication (internet sites and social network profiles - Facebook and Twitter) of ministries of foreign affairs of the observed states, based on the number of press releases, appearance, content and other relevant features: orientation to the monologic or dialogic model of communication, organization of web sites, interactivity, thematic categories as well as coordination with the thematic agenda of the most visited news portals. Furthermore, the online questionnaire was used to identify basic demographic, psycho-social, and socio-economic features of Internet users, who expressed their opinion on the activities of state institutions on the Internet and gave recommendations for their further development. Research included also interviews, which were organized with representatives of three groups of professions: diplomatic, scientific and media, with the aim of confirming and summing conclusions gathered through previous analysis of the literature, as well as online presence of selected countries on the internet and results of online questionnaire. This research confirms the hypothesis that the use of new media (also) in Croatia implies the necessity of reconceptualization of ways and content of public diplomacy, having in mind that public now has the possibility to directly comment foreign policy positions and activities, which was not the case in the time of domination of traditional media and traditional diplomacy, where the international politics was the field of activity of a closed circle of professional diplomats and experts. In a new situation, the diplomatic institutional structure is forced to develop professional, planning communication, both internal and external, based on the benefits of the concept of integrated communication and the elements of communication excellence.