The 21 species of sea ducks are one of the larger subgroups (Tribe Mergini) of the waterfowl family Anatidae, and the 16 species (one historically extinct) that are native to North America represent the largest number to be found on any continent. This book is an effort to summarize succinctly our current knowledge of sea duck biology and to provide a convenient survey of the vast technical literature on the group, with over 900 literature references. It includes 90,000 words of text (more than 40 percent of which is new), 15 updated range maps, 31 photographs, over 30 ink drawings, and nearly 150 sketches. Lastly, the North American sea ducks include the now extinct Labrador duck, the only northern hemisphere waterfowl species to have gone extinct in modern times. Considering recent population crashes in other sea ducks, such as the Steller's eider and spectacled eider, it should also offer a sobering reminder of the fragility of our natural world and its inhabitants, including us.