The Lowcountry (sometimes Low Country or just low country) is a geographic and cultural region along South Carolina's coast, including the Sea Islands. The region includes significant salt marshes and other coastal waterways, making it an important source of biodiversity in South Carolina.

Once known for its slave-based agricultural wealth in rice and indigo, crops that flourished in the hot subtropical climate, the Lowcountry is today known for its historic cities and communities, natural environment, cultural heritage, and tourism industry. Several dozen Native American tribes had inhabited the area, including the Cusabo (and sub tribes) and Etiwan. Demographically, the Lowcountry is still heavily dominated by African American communities, such as the Gullah/Geechee people.

As of the 2020 census, the population of the Lowcountry was 1,167,139.

The term "Low Country" originally referred to all of the states below the Fall Line, or the Sandhills, which run the width of the states from Aiken County to Chesterfield County. The Sandhills, or Carolina Sandhills, is a 15–60 km (9.3–37.3 mi) wide region within the Atlantic Coastal Plain province, along the inland margin of this province. The Carolina Sandhills are interpreted as eolian (wind-blown) sand sheets and dunes that were mobilized episodically approximately 75,000 to 6,000 years ago. Most of the published luminescence ages from the sand are coincident with the last glaciation, a time when the southeastern United States had colder air temperatures and stronger winds. The area above the Sandhills is known as "Upstate" or "Upcountry". These areas are different in geology, geography, and culture.

There are several variations in the geographic extent of the "Lowcountry" area. The most commonly accepted definition includes Charleston, Dorchester, Beaufort, Georgetown, Colleton, Hampton, Berkeley, Jasper, and Williamsburg Counties, often described as the area encompassing the basins of Cooper River, Santee River, ACE (Ashepoo-Combahee-Edisto), Winyah Bay, and Savannah River. Some include Marion and Horry Counties. Dillon County is included in the Lowcountry by the largest group of healthcare executives in the state. Allendale is also occasionally included in the region.

Four counties are covered by the Lowcountry Council of Governments, a regional governmental entity charged with regional and transportation planning, and are the ones included in the South Carolina Department of Parks, Recreation, and Tourism's "Lowcountry and Resort Islands" area. The area includes the Hilton Head Island-Bluffton-Beaufort, SC Metropolitan Statistical Area.

Technically, the Lowcountry is synonymous with the areas with a large population of Gullah Geechee peoples of the region. Gullah Geechee people have traditionally resided in the coastal areas and the sea islands of North Carolina, South Carolina, Georgia and Florida—from Pender County, North Carolina, to St. Johns County, Florida.

Coastal South Carolina’s half a million acres of salt marsh, which typifies the Lowcountry in particular, is underlain by plough mud or pluff mud, named for the traditional spelling of plow but now often pronounced to rhyme with rough. Once used to fertilize fields of cotton, the mud is pervaded by decaying organic matter and bacteria that feed on it, giving it a notoriously sulfurous stench.