The penal system is a system of punishment for perpetrators of criminal offenses with dual function: protection of the society from criminal offenses and re-socialization of perpetrators and reduction of recidivism. Throughout history, the need for re-socialization and postpenal reception of prisoners is increasingly emphasized. For the purpose of re-socialization, various individual and group treatments of prisoners are carried out. The main advantage of the group approach is mutual support and the development of interpersonal relationships. In group work, practitioners mainly use cognitive - behavioral techniques. The group of prisoners numbers small number of members and groups are closed, to make the work as efficient as possible. The groups are divided according to the characteristics of the users and the purpose of the treatment. There are groups for the treatment of drug addicts, alcohol addicts, for the treatment of sexual delinquents ... The ultimate goal is to change unwanted behavioral patterns into behavior that conforms to social norms.