This book constitutes the thoroughly refereed post-workshop proceedings of the 4th International Workshop on Modelling and Simulation for Autonomous Systems, MESAS 2017, held in Rome, Italy, , in October 2017. The 33 revised full papers included in the volume were carefully reviewed and selected from 38 submissions. They are organized in the following topical sections: M&S of Intelligent Systems – AI, R&D and Applications; Autonomous Systems in Context of Future Warfare and Security – Concepts, Applications, Standards and Legislation; Future Challenges and Opportunities of Advanced M&S Technology.