The mobile is a desirable object in adolescence, because it favors personal autonomy, especially with regard to their parents. Furthermore, cellular phone provides identity and prestige in comparison with their peers, offers the main technological innovations, is a source of fun and entertainment and it favors the establishment and maintenance of interpersonal relationships. All these characteristics are useful to explain the very intense link between the mobile phone and adolescents, and understand the significance that this instrument has acquired for them. This work has three objectives. First, to describe the pattern of use or abuse of the mobile in adolescence and analyse two of the main variables involved: sex and age. Second, to develop several instruments to evaluate the main characteristics related with the use, abuse, and dependence of mobile phone in adolescents. And third, to propose some recommendations in order to prevent mobile addiction in teenagers. The book is useful for all those persons or professionals (especially from educational, social and clinical fields) who are interested in understanding, identifying and preventing mobile phone addiction in adolescents.