With the vehicle architecture selected and the control system architecture defined, the focus then shifted to development and validation of the hybrid vehicle supervisory controller. The control system architecture was used to systematically outline the specific requirements of the control strategy for the hybrid vehicle supervisory controller. Contol software was then developed using Mathworks Simulink and Stateflow using a modular software architecture to facilitate team work and code reusability. To validate and improve the fuel economy optimization strategy a simple vehicle model was then developed. This low fidelity model was designed to meet the requirements for fuel economy while still allowing fast execution times. Finally a more detailed vehicle model was developed for safety critical validation of the hybrid vehicle supervisory controller software and hardware using hardware-in-the-loop testing. This testing method was demonstrated for fuel economy testing, performance improvement, safety critical testing, and diagnostic validation.