In recent years, the co-operation between industrial firms and universities has increased considerably, but the interaction pattern in different technological fields is not uniform. In science-based fields, university departments have a distinct focus on basic research and the major interest of industry is the observation of science. In less science-based fields, the solution of technical problems is a major concern of industry. In all fields, the exchange of knowledge in techno-scientific communities is a crucial element of interaction. In Germany, strong intra-disciplinary ties between universities and industry in mechanical engineering obviously imply an insufficient openness to, and integration of, new technologies. The particular combination of a long-standing culture of co-operation and the economic success in the mechanical industry can be interpreted in terms of a specific path-dependant evolution of a stable sector of the national system of innovation, but with the tendency to lock-in effects.