Eider may refer to:

• two genera and four species of birds in the duck subfamily Merginae:
  • Common Eider (Somateria mollissima)
  • King Eider (Somateria spectabilis)
  • Spectacled Eider (Somateria fischeri)
  • Steller's Eider (Polysticta stelleri)
• the downy feathers from these ducks, used to fill pillows, duvets, and other bedding.

• a river in Schleswig-Holstein, Germany; see Eider River

• a comic book character; see Eider Duck