Simulation and Modeling is one of the most important and widely used techniques in many research areas. The available simulation tools are mostly meant for standalone use and do not attempt to address the overall scenarios. It would be advantageous and cost-effective to combine these models thus forming a new integrated simulation model based on individual existing components to model complex scenarios and understand the joint effect of multiple phenomena. In this book, we discuss a framework to integrate multiple autonomous simulation models into an integrated environment wherein we can model and execute complex scenarios involving multiple simulators. Our techniques are implemented in RAISE (Reflective Architecture for Integrated Simulation Environments); specifically, we design meta-level synchronizer and data exchange modules that support flexible constraint specification while supporting high levels of concurrency in the execution.