This book describes how group treatment offers a unique opportunity for group members to learn and to change as they interact with other group members. The group structure presents a social microcosm of relationships that people who seek psychotherapeutic treatment find problematic in their private and public lives. In groups, the participants can observe each other, provide feedback to each other, and practice change strategies. In short, group treatment has a powerful healing and supportive function. Based on the authors’ many years of education and experience in academia, the private and public sectors, specific guidance is offered to group leaders on participation, organization, and communication in group treatment. The authors describe the history and characteristics of group treatment, how to organize a treatment group, the roles and responsibilities of the group leader, methods of group treatment, and typical responses of participants. Given its purpose and methodology, this book takes an original perspective on group treatment aimed ultimately at improving healing processes in healthcare and social care. This book will provide a helpful introduction and guide for a range of professionals who work in primary healthcare, company healthcare, somatic care, psychiatric and social care, and the non-profit sector.