Based on production volume and value and on per capita consumption, shellfish are an important food group in the United States. The nutrient composition of shellfish indicates that this food group is low in fat and relatively high in protein. Tabulated data on fatty acids in the different edible portions of seven species of crustaceans and over twenty species of mollusks are presented. The proportionately high level of polyunsaturated fatty acids is shown by the polyunsaturation index calculated for some important species of shellfish.