N-3 Fatty acids are essential compounds in higher eukaryotes and are linked to various health benefits in humans including cognitive and visual development of infants and reduced risk of cancer, cardiovascular diseases and mental illnesses of adults. Several health authorities and professional organisations have made dietary recommendations for intake of n-3 fatty acids to achieve nutrient adequacy and prevent and treat chronic diseases, e.g. cardiovascular diseases. This book reviews the recent knowledge of nutritional needs and sources of n-3 fat and presents production strategies for microbial DHA and EPA production.