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 Skholm, 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 environment now includes novel, dynamic approaches such as mobility, wearability, ubiquity, ad hoc use, mindhody orientation, and businesslmarket ori- tation. This modem environment challenges the whole information security research community to focus on interdisciplinary and holistic approaches whilst retaining the benefit of previous research efforts. Papers offering research contributions focusing on dynamic environments in addition to other aspects of computer security and privacy were solicited for submission to IFIPISEC 2006. We received 141 submissions which were all reviewed by at least three members of the international program committee.