This chapter discusses the natural hazards associated with developments on barrier islands. The resolution of conflicts regarding barrier island utilization must be based on a full understanding of the dynamic nature of these islands. The chapter attempts to provide such an understanding by reviewing the state of knowledge regarding the physical processes that have led to the development of barriers, and the natural forces of sediment dispersal which continue to modify them. It provides the scientific basis for an optimum utilization of America's barriers, recognizing that their role in our economy derives from their recreational, scenic, ecologic, and strategic values. The discussion of barrier island stratigraphy, morphology, and sedimentation has revealed that the knowledge now exists to provide scientific input into plans for the optimum utilization of this fragile coastal ribbon of sand. The barrier islands have evolved according to physical laws. Their morphology is a predictable response to external environmental parameters.