Opinion leaders have an influence on others and can bring about changes in opinion and behavior. Due to everyday stimulus and information overload, they play an important role in personal decision-making processes such as purchasing decisions. For companies and advertisers, opinion leaders have also become an important target group due to new forms of marketing such as word-of-mouth and viral marketing. Matthias Dressler and Gina Telle first analyze existing theories and models on opinion leadership. They explain the development of research on this topic and its impact on existing communication models. Their analysis focuses on functions, motives and effects of opinion leadership. In addition, methods for identifying opinion leaders and opinion leaders in the diffusion process are presented.