Whereas the development of test methods for fracture mechanics of composite laminates has reached a high level of maturity in recent years, relatively little attention has been given to the development of fracture mechanics test methods for sandwich composites. Of the limited number of investigations performed to date, a majority have emphasized a particular sandwich material or the effects of specific environmental conditions. In general, the test methods proposed for fracture mechanics of sandwich composites have been found to be problematic due to problems in testing, crack propagation, and the analysis of test data. Emphasis in this research project grant will be focused on the development of fracture mechanics test methods for sandwich composites. The ultimate goal of the proposed research is to establish draft ASTM standards for both Mode I and Mode II fracture toughness of sandwich composite materials.