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