Eicosapentaenoic acid, EPA, is a long-chain omega-3 polyunsaturated fatty acid with 20 carbon atoms and 5 double bonds, found principally in oily fish such as mackerel, sardines, and salmon, and in fish oil supplements alongside docosahexaenoic acid. It serves as a precursor to anti-inflammatory eicosanoids including prostaglandins and resolvins, and is associated with reduced risks of coronary heart disease and improved triglyceride profiles. Its multiple double bonds make it highly susceptible to oxidation, so fish oils require antioxidant protection, oxygen-barrier packaging, and cold storage to prevent rancid off-flavours. Regulatory bodies have approved qualified heart-health claims for EPA-containing products, cementing its role in functional foods and nutraceuticals.