Estuarine habitat in Georgia is under increasing threat of degradation, which can negatively impact ecologically and commercially important species that reside there. Blue crabs (Callinectes sapidus) are the second highest valued fishery in Georgia yet little is known about their essential habitat requirements within either subtidal or intertidal areas. Ultrasonic telemetry was used to track 57 crabs, over 4 years, in the Duplin River estuary, near Sapelo Island, GA in order to assess movement patterns and habitat use. Crabs tagged with ultrasonic transmitters ranged in size from 4 to 13.3 cm CW and varied in sex and ontogenetic stage. Crab locations, substrate type, depth, and molting habitat was organized and analyzed within a geographic information system 2(GIS). Reproductively mature females used the greatest total area 1,052 m on average over 8 days and movement was emigrational at average speeds of 657 m/day out of the estuary into the higher salinity Doboy sound. Male crabs did not, on average, use as 2large an area 108 m on average over 7 days and movement patterns showed a high degree of meander and retention within the system. Movement speeds averaged 82 m/day. Immature female crabs were intermediate with a larger degree of meander than mature females with average movement speeds of 150 m/day, but used less total area 2(157 m on average over 8 days). Crabs were tracked going onto and off of the flooded vegetated marsh surface and found on patches of oyster reefs located along edges of the subtidal zone indicating their habitat use. Crabs tagged with specialized molting transmitters were tracked to their molting habitat, which consisted of the vegetated marsh surface. The use of vegetated marsh edge is very important to crabs and was recoded frequently among all sexes and sixes of crabs. The adjacent marsh, therefore, is an essential part of blue crab habitat, it defines the subtidal creek habitat and provides essential habitat for molting crabs.