This book constitutes the thoroughly refereed post-proceedings of the IFIP-TC6 6th Annual International Working Conference on Active Networks, IWAN 2004, held in Lawrence, KS, USA in October 2004. The 14 revised full papers presented together with 1 invited paper were carefully reviewed and selected from 32 submissions. The papers are organized in topical sections on active networking systems, active networking security, active networking applications, mobile active networks, and active networking management.