Protecting critical infrastructures, such as electrical power grids, has become a significant concern for many nation states in recent years. Increasing attention is being given to the problem of infrastructure modeling, in order to help identify and redress potential vulnerabilities. Understanding critical infrastructure behavior involves modeling not only individual infrastructures, but also the dependencies that can exist across related infrastructures. Our research adopts a multi-dimensional approach to critical infrastructure modeling that employs Cougaar as the central architecture for agent-based integration of heterogeneous modeling knowledge, both within and more importantly across infrastructures. This paper presents an overview of our research, describes the integration of Cougaar in the overall modeling environment under development, and outlines our experiences with Cougaar in the development process.