Symbiotic Simulation (S2) is a relatively new and uninvestigated area. It utilizes simulations to control, optimize a system or give support to the decision maker or the system itself in real-time. The S2-system is connected to the physical system (real-world) and uses Modeling and Simulation tools for simulating it or its entities. Thus predicting the effect of choosing different course of actions by comparing the outcomes of several so called what-if simulations. The result of the simulations are applied to the physical system and thereby improving it. This relation between the simulations and the physicals system is mutually beneficial which justifies the name Symbiotic Simulation. The on-line connection of simulation and physical system implies new requirements on the M&S process and the main objective of this project is to study them. Three different activities in this area are presented in this report.The first activity studies the applicability of Symbiotic Simulation in path planning of UAVs, employinga software simulator called S2-Simulator. The second activity studies the connection between the physical system, in this case the Command and Control System and the Symbiotic Simulation. In this part the existing ISTAR (Intelligence Surveillance Target Acquisition and Reconnaissance) system is investigated as a case-study. In the third activity a concept of using Embedded Simulation to support predictive situation awareness of commander in riot situations and plan recognition is introduced. The report finishes with general conclusions and possible future work.