The main theme of the thesis are social networks which has become more and more significant communication means these days. It mainly focus on the "public" and "private" categories that appear at social networks - especially on Facebook. Theory brings different views of traditional authors Hannah Arendt and Jürgen Habermas based on antagonistic nature of this dichotomy - public and private. These approaches are complemented by a modern concept of an american anthropologist Susan Gal, which serves as an alternative. The second part deals with the qualitative research and its results that show how Facebook users percieve and build private and public areas on this social network. Where is the border between them and if there is a possibility i...