Selenium (Se) is an essential dietary trace element participating in the regulation of various physiological functions in humans, farm animals and poultry through its incorporation into a range of selenoproteins. Low Se content in main feed ingredients is a common problem worldwide and dietary Se supplementation is a current practise in pig nutrition. Recent research clearly proved that sodium selenite, used as a feed supplement for the last 45 years, is not an optimal form of Se. However, use of organic selenium in pig diets can help meeting Se requirement and maintain health/high immunocompetence, productive and reproductive performance.The goal of this book is to provide up to date information about the roles of Se in pig nutrition and health. The role of selenium as an essential part of the integrated antioxidant system gets special attention. Organic Se concept in pig nutrition is described in detail with emphasis to selenomethionine as a storage form of Se in the body and to selenocysteine, the active form of selenium within the selenoproteins. Specific Se-deficiency related disorders in pigs are also described, and the importance of Se in growth, development, immunity and reproduction is demonstrated. Molecular mechanisms of protective effects of Se under stressful conditions of commercial pig production are characterised.This book will be of practical importance to pig producers, to nutritionists and vets as well as for pig/animal scientists, students of agricultural colleges and universities. It will also be of interest for researchers in areas related to ecology, environmental sciences, food sciences, etc.