According to the World Health Organisation, pathological addiction is the psychic, and sometimes even physical, condition arising from the interaction between a living organism and an exogenous substance, characterised by behavioral responses and other reactions that always include a compulsive need to take the substance continuously or periodically, in order to get its psychic effects and/or to avoid the distress related to its withdrawal. This book presents a review on Internet addiction, which is considered an emergent problem especially amongst adolescents, and examines the risk factors and health effects of this addiction.