The Atlantic Coastal Plain aquifer system, which underlies a large part of the east coast of the United States, is an important source of water for more than 20 million people. As the population of the region increases, further demand is being placed on those ground-water resources. To define areas of past and current declines in ground-water levels, as well as to document changes in those levels, historical water-level data from more than 4,000 wells completed in 13 regional aquifers in the Atlantic Coastal Plain were examined. From predevelopment to 1980, substantial water-level declines occurred in many areas of the Atlantic Coastal Plain. Regional variability in water-level change in the confined aquifers of the Atlantic Coastal Plain resulted from regional differences in aquifer properties and patterns of ground-water withdrawals. Within the Northern Atlantic Coastal Plain, declines of more than 100 ft were observed in New Jersey, Delaware, Maryland, Virginia, and North Carolina. Regional declines in water levels were most widespread in the deeper aquifers that were most effectively confined?the Upper, Middle, and Lower Potomac aquifers. Within these aquifers, water levels had declined up to 200 ft in southern Virginia and to more than 100 ft in New Jersey, Delaware, Maryland, and North Carolina. Substantial water-level declines were also evident in the regional Lower Chesapeake aquifer in southeastern New Jersey; in the Castle Hayne-Piney Point aquifer in Delaware, Maryland, southern Virginia and east-central North Carolina; in the Peedee-Severn aquifer in east-central New Jersey and southeastern North Carolina; and in the Black Creek-Matawan aquifer in east-central New Jersey and east-central North Carolina. Conversely, declines were least severe in the regional Upper Chesapeake aquifer during this period. In the Southeastern Coastal Plain, declines of more than 100 ft in the Chattahoochee River aquifer occurred in eastern South Carolina and in southwestern Georgia, where water levels had declined approximately 140 and 200 ft from prepumping conditions, respectively. Within the Upper Floridan aquifer, decline was most pronounced in the coastal areas of Georgia and northern Florida where ground-water withdrawals were at their highest. These areas included Savannah, Jesup, and Brunswick, Ga., as well as the St. Marys, Ga. and Fernandina Beach, Fla., area. Regional water levels had declined by 80 ft near Brunswick and Fernandina Beach to as much as 160 ft near Savannah. Since 1980, water levels in many areas have continued to fall; however, in some places the rate at which levels declined has slowed. Conservation measures have served to limit withdrawals in affected areas, moderating or stabilizing water-level decline, and in some cases, resulting in substantial recovery. In other cases, increases in ground-water pumpage have resulted in continued rapid decline in water levels. From 1980 to 2000, water levels across the regional Upper, Middle, and Lower Potomac aquifers continued to decline across large parts of Delaware, Maryland, Virginia, and North Carolina, and water levels had stabilized or recovered throughout much of Long Island and New Jersey. Substantial water-level recovery had also occurred in east-central New Jersey in the Peedee-Severn and Black Creek-Matawan aquifers and in east-central North Carolina in the Castle Hayne-Piney Point aquifer. Substantial declines from about 1980 to about 2000 occurred in the Peedee-Severn aquifer in southern New Jersey, the Beaufort-Aquia aquifer in southern Maryland, and the Black Creek-Matawan and Upper Potomac aquifers in central and southern parts of the coastal plain in North Carolina. From 1980 to about 2000, water levels within the regional Upper Floridan aquifer had generally stabilized in response to shifting withdrawal patterns and reductions in pumpage at many places within the coastal region. Ground-water levels had stabilized and recovered at the ma