The continuous development in communication and information technologies, together with an increasingly global marketplace, bring about a row of new marketing opportunities and challenges for businesses. Word of mouth, an exchange of information about products and services among consumers, presents both a potential threat and a route to success. Greatly encouraged by the information overload consumers experience today and the access to a variety of online channels of self-expression, word of mouth is a factor that businesses cannot ignore. In this book, we will first gain a deeper understanding of word of mouth as we explore its structural and psychological backgrounds and the prerequisites for its appearance. After that, we will explore the potential of word of mouth for marketing purposes and look into the channels available to marketers both on the internet and offline. Finally, to assess the impact and possible use of word of mouth in real business, we will look at an empirical study conducted together with Elektrika.cz, an online information portal in the Czech Republic.