Internet addiction (IA) was introduced as a new disorder in mid-1990s. Since then, there is growing concern about the addictive nature of the Internet. This chapter is a comprehensive review of published seminal, research and review papers, meta-analyses and book chapters/books on IA in adolescents. The conceptualization of IA, epidemiology, phenomenology, screening, diagnoses, treatment and prevention are discussed with relevant references. The concept of IA is at fetal level with no consensus on definition, norms or clinical criteria. Asian countries such as China and South Korea are affected most. A multination meta-analysis estimated an overall prevalence of 6% for IA. Most of the research identifies IA in gaming, gambling, social networking and cybersex. A few assessment tools have been used with no comparability or cultural sensitivity. Diagnostic criteria are proposed based on those used for substance abuse and pathological gambling. The treatments are mainly psychological with a lot of emphasis on cognitive behavior therapy. The Internet is a very versatile and useful tool for children and adolescents, and it is not advisable to ban it totally. The review highlights education of them on sensible Internet use and supports inclusion of IA in international disease classifications.