This paper will discuss via case study both military and civilian hybrid vehicle development focusing on the processes required from the selection of the hybrid propulsion system architecture, component downselection using advanced modeling and simulation tools, body/chassis development and integration, design verification testing using an advanced dynamometer test facility, and final full vehicle validation on the test track. The paper will incorporate results from the FED (Fuel Efficiency Demonstrator) program where AVL is responsible in collaboration with World Technical Services Inc., for delivering a fully developed hybrid propulsion system integrated into the demonstrator vehicle.