During the last years man efforts have been devoted to inspect the inter-dependence among Critical Infrastructures. Even assuming that the asset owners are supposed to handle their own possible misbehaviours properly, critical events maybe triggered by infrastructure's interactions. Therefore the need to handle and possibly measure inter-dependencies. Within this perspective, the EU funded MIA Project which basic aim is to assess some measures to quantify inter-dependencies among Critical Infrastructures (energy and ICT networks) for the topological and the service level. We report recent outcomes of that project based on topological information and especially on spectral analysis that can be related to dynamical properties of the electric and telecommunication systems. A topological concepts of "Relevance" is applied for the first time to the real electric network of Roma area. © 2010 IEEE.