This book contains the Proceedings of the 21st IFIP TC-11 International Information Security Conference (IFIPISEC 2006) on "Security and Privacy in Dynamic Envir- ments" held in May 22-24 2006 in Karlstad, Sweden. The first IFIPISEC conference was arranged in May 1983 in Stockholm, Sweden, one year before TC- 1 1 was founded, with the active participation of the Swedish IT Security Community. The IFIPISEC conferences have since then become the flagship events of TC-11. We are very pleased that we succeeded with our bid to after 23 years hold the IFIPISEC conference again in Sweden. The IT...