The evolution of the Internet has led us to the new era of the information infrastructure. As the information systems operating on the Internet are getting larger and more complicated, it is clear that the traditional approaches based on centralized mechanisms are no longer meaningful. One typical example can be found in the recent growing interest in a P2P (peer-to-peer) computing paradigm. It is quite different from the Web-based client-server systems, which adopt essentially centralized management mechanisms. The P2P computing environment has the potential to overcome bottlenecks in Web computing paradigm, but it introduces another difficulty, a scalability problem in terms of information found, if we use a brute-force flooding mechanism. As such, conventional information systems have been designed in a centralized fashion. As the Internet is deployed on a world scale, however, the information systems have been growing, and it becomes more and more difficult to ensure fau- free operation. This has long been a fundamental research topic in the field. A complex information system is becoming more than we can manage. For these reasons, there has recently been a significant increase in interest in biologically inspired approaches to designing future information systems that can be managed efficiently and correctly.

This volume of the LNCS series contains the proceedings of the 5th Internat- nal Working Conference on Active Networks (IWAN 2003) held in the ancient cultural city of Kyoto, Japan. This year we received 73 submissions. The increasing number indicates that Active Networks continues to be an attractive ?eld of research. Through - reful reviewing and discussion, our program committee decided to fully accept 21 papers. Three papers were conditionally accepted, and were included after shepherding by members of the technical program committee. This volume thus includes these 24 papers which were presented at IWAN 2003. Additional papers were presented in a poster session at the conference. The best paper award went to Kenneth L. Calvert, James N. Gri?oen, - jati Imam, and Jiangbo Li (University of Kentucky) for "Challenges in Imp- menting an ESP Service," which begins these proceedings and which began the papers in the High Performance & Network Processors session. Papers in these proceedings are organized into seven sessions: High-Level Active Network - plications, Low-Level Active Network Applications, Self-Organization of Active Services, Management in Active Networks, Experiences with Service Engin- ring for Active Networks, and Selected Topics in Active Networks, ranging from risk management to context-aware handover and peer-to-peer communications.

This book constitutes the refereed proceedings of the IFIP-TC6 Third International Working Conference on Active Networks, IWAN 2001, held in Phildelphia, PA, USA in October 2001.The 10 revised full papers presented were carefully reviewed and selected from 22 submissions. Papers presented covered topics like active multicast, active QoS, active security, active GRIDs, management, architectures, language and API issues.