This book constitutes the refereed proceedings of the First International Workshop on Active Networks, IWAN'99, held in Berlin, Germany in June/July 1999. The 30 revised full papers presented were carefully reviewed and selected from a total of 80 submissions. The book is divided in sections on networks architectures, platforms, active management and control, and security. All in all, this book provides a unique state-of-the-art account of architectural aspects, technologies, and prototype systems that will impact the way future networked businesses will be created and managed.