The more our society relies on electronic forms of communication, the more the security of these communication networks is essential for its well-functioning. As a consequence, research on methods and techniques to improve network security is extremely important. Topics in this volume include the developments in: security protocols; secure software engineering; mobile agent security; e-commerce security; and security for distributed computing.; This title contains the proceedings of the First International Working Conference on Network Security (I-NetSec 01), which was sponsored by the International Federation for Information Processing (IFIP), and held in Leuven, Belgium in November 2001.