The Weddell Sea is part of the Southern Ocean. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. Much of the southern part of the sea, up to Elephant Island, is permanent ice, the Filchner-Ronne Ice Shelf. The entire sea is part of the Argentinian claim in Antarctica. At its widest the sea is around 2,000 km, in area it is around 2.8 million km²

The sea is named after the British sailor James Weddell who entered the sea in 1823 as far as 74° S. It was first widely explored by the Scot William S. Bruce over 1902-04. In was in this sea that Shackleton's ship, the Endurance was trapped and crushed by ice.

It is believed that the break-up of Gondwana started in the Weddell Sea.