Dietary fatty acids serve many roles; they are a component of triglycerides and also serve as precursors to prostaglandins and other eicosanoids. The essential (ie, required) fatty acids in canine and feline diets include omega-6 and omega-3 fatty acids. The omega-6 acid linoleic acid (LA) is required for dogs and cats, and arachidonic acid (AA) is also required for cats. Omega-3 fatty acids include eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and α-linolenic acid (ALA). Marine oil sources provide EPA and DHA, which are more effective in dogs and cats than ALA (which is not significantly converted to EPA or DHA). The eicosanoids produced from omega-3 fatty acids are less inflammatory than those produced from AA. As discussed here, marine oil fatty acids have been useful in many clinical conditions.