Dr.-Ing. Günter Schäfer studied computer science at the Universität Karlsruhe, Germany, from 1989 to 1994. After his studies he continued there as a member of the scientific staff at the Institute of Telematics. He received his doctorate on the topic Efficient Authentication and Key Management in High-Performance Networks in October 1998. In February 1999 he took a postdoctoral position at the Ecole Nationale Supérieure des Télécommunications in Paris, France, where he focused on network security and access network performance of third-generation mobile communication networks. Since August 2000, he has been at the Technische Universität Berlin, Germany, where he is involved in research and lectures on the subject of telecommunications networks. His main subject areas are network security, mobile communications, and active network technologies. Dr. Günter Schäfer is a member of the Institute of Electrical and Electronics Engineers (IEEE) and the Gesellschaft für Informatik (German Computer Science Society).