This book constitutes the thoroughly refereed post-conference proceedings of the Third International Workshop on Critical Information Infrastructures Security, CRITIS 2008, held in Rome, Italy, in October 2008. The 39 revised full papers presented were carefully reviewed and selected from a total of 70 submissions. All the contributions highlight the current development in the field of Critical (Information) Infrastructures and their Protection. Specifically they emphasized that the efforts dedicated to this topic are beginning to provide some concrete results. Some papers illustrated interesting and innovative solutions devoted to understanding, analyzing and modeling a scenario composed by several heterogeneous and interdependent infrastructures. Furthermore, issues concerning crisis management scenarios for interdependent infrastructures have been illustrated. Encouraging preliminarily results have been presented about the development of new technological solutions addressing self-healing capabilities of infrastructures, that is regarded as one of the most promising research topics to improve the infrastructures’ resilience.