The Late Holocene geologic history of St. George Island was interpreted through the study of surface geomorphic features, subsurface stratigraphic data, and an investigation of coastal processes operative during historical times. Subsurface data from Rattlesnake Point and Goose Island show three distinct units, interpreted to be offshore silty sands, open lagoon or sound sands, and clean sands of barrier island, spit, and platform origin. A general up-core and seaward increase in the sand to silt ratio indicates that there was an influx of offshore sands to the area. This and subsurface data from the literature suggest that offshore sources Supplied the sands for the formation of St. George Island. Gap Island probably emerged on a small shoal about 3,500 years B.P., and then prograded seaward by successive beach ridge accretion. Geomorphic and stratigraphic evidence suggest that St. George Island proper developed later, probably growing together from two newly emergent island nuclei. The mechanism that can most easily explain the emergence of these three original island cores is a fluctuating or oscillating sea. Since its inception, landward migration of the island has been minor, certainly not being even as much as the island's width. There has been some migration as is demonstrated by the many overwash features, a large migrating dune wave, and the welding of St. George Island onto Gap Island. Statistical analyses of the granulometry of the Gulf beach sands, used in conjunction with mapping techniques (i.e. bathymetric differencing and Log-log profiles), indicate that the dominant direction of sand transport is shore-normal, although shore-parallel transport does appear to operate within definable littoral cells or sub-cells. Shoreface erosion has been variable along the island, with landward shoreline translation ranging from less than 25 meters to nearly 250 meters between the years 1873-1943. This was not accompanied by lagoon shoreline aggradation, so that the result was a narrowing of the island. Much of the sands involved in shoreface erosion have apparently been going offshore, thus maintaining or even decreasing the offshore and shoreface profile.