Like most other sea ducks, male common eiders (Somateria mollissima) concentrate in large groups to molt following the breeding season. Although Maine conducted surveys in the 1980s, little was known of eider molting sites in Atlantic Canada until recently, when surveys and research conducted in Quebec, Newfoundland, Labrador, Nova Scotia and Maine revealed a number of important molting sites. Sites vary in importance from a few hundred males to tens of thousands. Important sites include the western and southern coastal areas of Anticosti island (40,000 birds), Baie des Milles Vaches (9,000) in Quebec, southwestern Nova Scotia (40,000), Petit Manan Island archipelago (7,000), and Metinic Island archipelago (10,000) in Maine. Molting eider surveys conducted in Maine during the early 1980s and in the St. Lawrence in 2003-2004 revealed large flock sizes, commonly over 2,000 birds, in consistent locations annually. An estimated 40,000 males molt in Nova Scotia and 28,400 in Maine (1981 data). Surveys indicate that important sites are used consistently between years and that local movements occur. Recoveries from banded birds suggest that eiders breeding on the lower North Shore of the St. Lawrence, New Brunswick, Nova Scotia, and even Newfoundland appear to concentrate at the Petit Manan site in Maine. They also suggest inter annual movements between the Nova Scotia and Petit Manan sites. Greater understanding of the relationships between breeding, wintering, and molting sites will facilitate management of this heavily exploited sea duck.