Book excerpt: Primarily, a review on theoretical foundations and the history of Viral Marketing is shown. Based on this, different definitions were analysed to set up a practical definition for this study. Thereafter, possible targets of Viral Marketing are illustrated, followed by necessary elements of Viral Marketing campaigns and finally by an approach to measure the effectiveness. By means of an online questionnaire, a survey was conducted to collect empirical data. These data provide information about Viral Marketing within social networking sites and detect useful information for the practical use of Viral Marketing. The results of the analysis show the accelerating influence of social networking sites and other factors regarding the effectiveness of Viral Marketing. In addition, specific characteristics which make Viral Marketing messages appealing as well as the preferred types of Viral Marketing messages are illustrated. They help to understand how to create and design an effective Viral Marketing Campaign.