The 5th Polish-German Teletraffic Symposium (PGTS '08) takes place in Berlin. It continues a series of events held every two years (Dresden 2000, Gd'ansk 2002, Dresden 2004, Wroclaw 2006). PGTS has been created to fasten the cooperation between the telecommunications and teletraffic communities of the two neighbor-ing countries. Since 2000, PGTS has become a well-established international forum attracting contributions and participants not only from Germany and Poland but also from all over Europe. Teletraffic Theory and Engineering has a long tradition in both countries in the academic world of universities, academies, research institutions, and also within the telecommunications industries and within network operating organizations. The Polish teletraffic community holds annual meetings (Polish Teletraffic Symposia) since many years, which are since 2000 interleaved with the PGTS meetings. The German teletraffic community is mainly organized in a Special Expert Group on System Architecture and Traffic Engineering within the German Information Technology Society (ITG) which organizes regular workshops and conferences and which considers itself as a national counterpart to the International Teletraffic Congress and its organizations. Teletraffic problems have changed substantially during the recent years as a result of the changes in the telecommunications area towards integrated digital networks, data services, internet and mobile communications. Traffic patterns have changed giving rise to more sophisticated traffic models and more advanced analysis methods, traffic and performance management. Despite all that, the fundamental issues as resource management, quality of service, traffic control or network planning and operation are still of key importance, where stochastic processes, simulation techniques and optimization methods are applied. PGTS '08 reflects almost all current areas of teletraffic research and engineering and, for the first time, also the upcoming field of network security. The organizers hope that PGTS '08 will contribute to the teletraffic science and be attractive for all categories of experts from theory to applications, from academic to industrial and network operators, and, especially, for promising young talents. PGTS may also act as a catalyzer for more joint research cooperations between Poland, Germany and other parts of Europe.