This volume contains the proceedings of the Third International Workshop on Critical Information Infrastructure Security (CRITIS 2008),which was held - tober 13-15, 2008 in Villa Mondragone (Rome), Italy, and was co-organized by AIIC (The Italian Society of Critical Infrastructures Experts) and ENEA (The Italian National Agency for New Technology, Energy and the Environment). This year's workshop was focused on an interdisciplinary and multifaced - alogue about the third millennium security strategies for critical information infrastructures (CII) and their protection (CIP). The aim was to explore the new challenges posed by the CII, bringing together researchersand professionals from universities, private companies and public administrations interested in all security-related aspects, and actively involved in the scienti?c communities at a national, European and trans-European level. More than 70 papers were submitted to the conference, which were screened by a very selective double-blind review process to identify the 39 papers selected for presentation, based on their signi?cance, novelty and technical quality. - visions were not checked and the authors bear full responsibility for the content of their papers. CRITIS 2008 also had six outstanding invited speakers: Erol Gelenbe (- perial College, UK), Massoud Amin (University of Minnesota, USA), George Apostolakis(MIT,USA),AndreaValboni(Microsoft,Italy),SujeetShenoi(U- versity of Tulsa, USA) and Angelo Marino (DG Information Society and Media, European Commission).