Barrier islands within bays, lagoons, estuaries and other protected waters have never been the subject of systematic research on a large scale. Within both the Chesapeake and Delaware Bays, barrier islands are numerous and widely distributed. Totaling more than 300 in number, these fetch limited barrier islands exhibit a range of morphologies uncommon along open ocean shorelines. We group the barrier islands in the two bays into three primary categories based on their morphology and location. In general, they are much shorter (~1km), narrower (<25m), and lower (1-2m) than their open ocean analogs, yet they behave in much the same way in their response to oceanographic processes. The greatest difference between ocean and bay barriers is the strong control of evolutionary processes by vegetation, usually salt marsh, in the bays.