In this thesis all media forms used in advertising campaigns by mobile network operators in Croatia are elaborated. Vipnet and Tele2 are chosen to be used as examples. The reasons for choosing particular forms of media are perceived. The process of development of the most frequently used media in advertising campaigns of mobile network operators in Croatia is elaborated. Different capabilities of particular media according to their advantages and disadvantages are displayed. The examples are corroborated with the current mobile network operators advertising campaigns and with that the elements are displayed within the possibilities of particular media to accomplish cognizable properties. Some of the principles of design that can be applied in the advertising campaigns of Vipnet and Tele2 are chosen. They represent two out of three mobile network operators on the Croatian market. The principals are indicated and they are used to analyze the corporate identity of the listed mobile network operators and to point out the strength of creativity in advertising. Vipnet and Tele2 use the principles stipulated in this thesis with quality and always in a recognized manner. The two companies have different approaches to using the principles of design, in this thesis that is pointed out and visually corroborated.