This book constitutes the thoroughly refereed post-conference proceedings of the Second International Workshop on Critical Information Infrastructures Security, CRITIS 2007, held in Benalmadena-Costa, Spain, in October 2007 in conjunction with ITCIP 2007, the first conference on Information Technology for Critical Infrastructure Protection. The 29 revised full papers presented were carefully reviewed and selected from a total of 75 submissions. The papers address all security-related heterogeneous aspects of critical information infrastructures and are organized in topical sections on R&D agenda, communication risk and assurance, code of practice and metrics, information sharing and exchange, continuity of services and resiliency, SCADA and embedded security, threats and attacks modeling, as well as information exchange and modeling.