The main objective of this thesis is to acquaint the reader with basic matters of social networks and their use for marketing purposes. The theoretical part describes the history, current trends and various tools throughout the entire online marketing. It also identifies a selection of chosen social networks - Facebook, Twitter and YouTube. The practical part is focused on the safety in publishing personal informations on the internet and marketing features on social networks. A survey was conducted amongst active users in order to gather information about their level of knowledge concerning safety on the internet. The contribution of this work is to explain the marketing process with possible evaluation of success and overall understanding...