SEDRIS is a technology that is developed as part of DMSO M&S Master Plan along with technologies like HLA. SEDRIS is designed to be a framework for representing synthetic environments. The framework specifies an unamiguous representation of the environment along with a lossless exchange schema for environmental data. A unified view of the environment facilitates interoperability among heterogeneous simulations and promotes a "fair fight". This report discusses basic concepts for modeling and simulation, primarily focused on distributed simulation and interoperability. Furthermore, the term "Synthetic environment" is defined, along with issues regarding integrating synthetic environments into simulations. The concepts of SEDRIS, its technology and development are thoroughly discussed, along with the current M&S situation in Sweden.