This book constitutes the thoroughly refereed post-conference proceedings of the 8th International Conference on Modelling and Simulation for Autonomous Systems, MESAS 2021, held as a virtual event due COVID-19, in October 2021.The 30 full papers together with 2 short papers included in the volume were carefully reviewed and selected from 50 submissions. They are organized in the following topical sections: M&S of intelligent systems,  R&D and application; and AxS/AI in context of future warfare and security environment and future challenges of Advance M&S Technology.