This is a keynote talk and the second of three papers presented at this conference. The first, “Systems Theory Background for Continuous/Discrete Integration” reviews some of the basic theory needed for this paper. Here we show how continuous and discrete modeling formalisms can be interfaced to support multiformalism modeling and simulation. Such a modeling approach is needed since typically natural systems are modeled in traditional differential equation terms while their controllers are best developed in more recent discrete formalisms. The third paper, “Distributed/Real Time Simulation: Integrating Legacy and Modern Codes”, provides an implementation perspective, addressing the major issue of legacy code reuse and its integration with modern code into advanced distributed computing systems.