Omega-3 polyunsaturated fatty acids (PUFAs) include a-linolenic acid (ALA; 18:3 omega-3), stearidonic acid (SDA; 18:4 omega-3), eicosapentaenoic acid (EPA; 20:5 omega-3), docosapentaenoic acid (DPA; 22:5 omega-3), and docosahexaenoic acid (DHA; 22:6 omega-3). In the past few decades, many epidemiological studies have been conducted on the myriad health benefits of omega-3 PUFAs. In this review, we summarized the structural features, properties, dietary sources, metabolism, and bioavailability of omega-3 PUFAs and their effects on cardiovascular disease, diabetes, cancer, Alzheimer's disease, dementia, depression, visual and neurological development, and maternal and child health. Even though many health benefits of omega-3 PUFAs have been reported in the literature, there are also some controversies about their efficacy and certain benefits to human health.