Internet is quickly getting into our normal lives and even into our intimate parts of our relationships. This book aims to describe the most common Internet-related behavior and connect it with clinical and empirical trends. We try to objectively describe basic paradigms, behavior patterns and explore the advantages and disadvantages of the on-line world. The book describes on-line and off-line communication methods and their impact on our relationships. We explore well-known and lesser-known phenomenons connected with cyberspace. All theoretical background is utilized in the empirical study of Czech adolescents and their addictive behavior.