This thesis investigates knowledge transfer at trade fairs and examines how private and official actors are involved in these processes. The thesis analyzes empirical findings from two case studies. Casa Pasarela which is a trade fair for home design, and Genera a trade fair for renewable energy. Both trade fairs took place in Madrid spring 2009 and were arranged by IFEMA. The theoretical approaches used in this thesis are concepts from evolutionary economics which mainly include types of knowledge, buzz, industrial knowledge bases, pipe lines and systems of innovation. The results demonstrate that knowledge transfer occurs different at trade fairs, and that buzz as a means for knowledge acquisition is diverse in industries. Firms in the design industry generally draw on a symbolic knowledge base. The knowledge in this industry is transferred in aesthetic symbols, images and signs which are related to trends, fashion and culture. Both buzz and face-to-face are relevant inputs for knowledge creation and allow exchange of tacit knowledge and information to take place at trade fairs. Firms in the energy industry draw in general on a synthetic knowledge base. They rely on tacit knowledge in the form of know-how and skills which are transferred face-to-face in formal relations. Informal buzz at trade fairs contains more an exchange of information which is less relevant for knowledge creation in this industry. The results also show that firms, government organizations, universities, trade fair organizers – actors of regional and national innovations systems, use foreign trade fairs to establish relationships for interactive learning and diffusion of innovations across national borders. Governments use trade fairs to present business opportunities in their domestic industry, and facilitate firms’ participation by arranging national common stands.