This thesis, titled „Prevention of addiction at schools. What can social work at schools contribute?“, deals with the topics addiction, prevention, and schools. Aim of this paper is to provide an overview of social work knowledge and methods to successfully execute prevention of addiction at schools. The first section summarizes the topic addiction. Causes of addiction are explained with the help of psychological, biological, sociological, and multi-attribute models. Moreover, legal regulations of adolescent’s drug use and specific youth addictions are discussed. The second chapter of this paper is dedicated to the youth target group. Characteristics of this phase of life such as the development stage and the environment of youth addicts and adolescent at risk of addiction are analyzed. Last but not least the interaction between schools and social work is described in the third section. Schools are referred to as the system whereas prevention is described as the foundation of social work. Finally, individual case help and group work are analyzed as the two biggest methods of systematic approach of social work dealing with prevention of addiction. The finding of this thesis is that social work can be extremely valuable for prevention of addiction at schools. Three identified success factors are extensive decision-making and responsibility, a variety of methods, and knowledge about addiction itself as well as the environment of today’s youth.