The protection of critical infrastructures, such as electrical power grids, has become a primary concern of many nation states in recent years. Critical infrastructures involve multi-dimensional, highly complex collections of technologies, processes, and people, and as such, are vulnerable to potentially catastrophic failures on many levels. Moreover, cross-infrastructure dependencies can give rise to cascading and escalating failures across multiple infrastructures. In order to address the problem of critical infrastructure protection, our research is developing innovative approaches to modeling critical infrastructures, with emphasis on analyzing the ramifications of cross-infrastructure dependencies. This paper presents an initial overview of the research and of the modeling environment under development.