This book constitutes the thoroughly refereed post-proceedings of the First International Workshop on Critical Information Infrastructures Security, CRITIS 2006, held on Samos Island, Greece in August/September 2006 in conjunction with ISC 2006, the 9th International Information Security Conference.

The 22 revised full papers presented were carefully reviewed and selected from a total of 57 submissions. The papers address all security-related heterogeneous aspects of critical information infrastructures. Thus dependence on this infrastructure and importance of its security is shown, emerging as a major objective for governments, companies and the research community.