The role of major dietary omega-3 fatty acids (Ω-3; α-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid) in human health has generated enormous scientific interest and many controversies in recent years. Due to a growing number of studies with conflicting or even negative clinical results, the former "hype" of Ω-3 thought to be beneficial in many aspects of human health regardless of the physiological and clinical preconditions is now being critically re-evaluated, especially with respect to the potential role of Ω-3 fatty acid supplementation in preventing a variety of diseases and clinical conditions. This critical view reflects the complex interaction of Ω-3 with cell membranes and their integrated proteins mediating signal transduction, transport systems, and other processes. Moreover, Ω-3 are precursors of bioactive metabolites, such as eicosanoids, lipoxins, resolvins, protectins, maresins, and nitrolipids that influence several physiological and pathophysiological processes and their full spectrum of effects are only beginning to be defined. Finally, physiological and pathophysiological conditions as well as concomitant pharmacological treatments may influence the specific and non-specific actions of Ω-3 supplementation. This Special Issue of the Journal of Clinical Medicine will emphasize the role and biological interactions of Ω-3 with regard to cancer, psychiatric disorders, metabolic disorders and nutrition and will also reflect on some basic molecular and cellular mechanisms.