The Distributed Interactive Simulation (DIS) system is an ambitious effort to take advantage of the tools of the information age to help improve the efficiency and effectiveness of the U.S. military services. Defined broadly, the DIS system is an infrastructure for linking simulations, simulators and live military systems of various types from any of the U.S. military services at multiple locations to create realistic, complex, virtual 'worlds' for the simulation of highly interactive activities. It poses serious challenges in the areas of technology, interservice coordination, and verification, validation, and accreditation (VV&A). This report concentrates on the validation challenge and presents a framework that encompasses all of the potential uses of the DIS system. It then illuminates the validation or credibility requirements for each type of use. Because of the breadth of the potential uses of DIS, the resulting framework is general enough to address any military application of models and simulations.