Meeting livestock nutritional requirements is extremely important in maintaining acceptable performance of neonatal, growing, finishing and breeding animals. In recent years a related feeding concept has been pursued. Conventional diet formulation is based on crude protein estimation with a safety premium in order to avoid amino acid malnutrition. Consequently higher excretion of nitrogen containing compounds is the result because protein supply is not matched as close as possible to the requirements. But increasing feed costs and environmental aspects have caused rethinking. It is possible to lower the crude protein content of a diet and provide the missing amino acids using supplemental amino acids. These diets are called low protein diets. This concept enables the producer to maintain animal performance while feeding a lower cost diet with less environmental burden. The objectives of this book are to clearly explain principles of animal nutrition to agriculture and animal science students and all those in livestock production and management.