Back Sound is a lagoon in eastern North Carolina that runs roughly east to west between Shackleford Banks to the south and the mainland and Harkers Island to the north. At its eastern end it meets Cape Lookout and Core Sound, and to the west it extends toward Beaufort and Bogue Sound along the Crystal Coast. Connected to Onslow Bay by Barden Inlet in the east and Beaufort Inlet in the west, it forms part of the shifting coastal waters of the Outer Banks region. Many islands within Back Sound are protected in the Rachel Carson Estuarine Reserve, which helps safeguard the Banker horses living on these marshy islands.