The goal of this book is to provide up to date information about the roles of Se in poultry nutrition and health. A special emphasis is given to the role of selenium as an essential part of the integrated antioxidant system. Se in feed and organic Se are characterised in detail with emphasis to selenomethionine as a storage form of Se in the body. Also specific Se-deficiency related diseases in poultry are described and the importance of Se in growth, development, immunity and reproduction is demonstrated. A link between poultry industry and human health via production of Se-eggs and Se-enriched meat is shown.