This paper discusses the latest techniques in vehicle modeling and simulation to support ground vehicle performance and fuel economy studies, enable system design optimization, and facilitate detailed control system design. The Autonomie software package, developed at Argonne National Laboratory, is described with emphasis on its capabilities to support Model-in-the-Loop, Software-in-the-Loop (SIL), Component-in-the-Loop (CIL), and Hardware-in-the-Loop simulations. Autonomie supports Model-Based Systems Engineering, which is growing in use as ground vehicles become more sophisticated and complex, with many more subsystems interacting within the vehicle and the environmental conditions in which the vehicles operate becoming more challenging and varied. With the advent of hybrid powertrains, the additional dimension of vehicle architecture has become one of the design variables that must be considered. This complexity results in the need for a simulation tool that is capable of incorporating systems of various levels of detail and fidelity, as well as handling scalable simulation tasks, from individual component models up to complete vehicles. Autonomie automates the process of building system simulations comprising the models chosen by the user, and then executes those simulations, producing tabular and graphical results. This capability eliminates the need for many of the manual steps that are normally encountered when creating and running a system simulation model. Specific applications are described to show the applicability of Autonomie to a wide range of problems. These applications highlight the use of Autonomie for SIL-based detailed control design using compiled production control software, ground vehicle performance and fuel economy optimization studies, and CIL testing at Argonne National Laboratory.