The nutrition of animals is undoubtedly a key factor, perhaps the most important one influencing their breeding. This is because, apart from playing a primary role in the manifestation of the genetic potential of animals, it significantly affects, more than any other factor, the cost of the produced animal products and their quality. This book examines the factors that influence, control, or regulate the productivity of animals, so that by utilizing them, the increase in animal production, the improvement of the quality of animal products, and the reduction of their production costs are achieved. Additionally, it aims at the production of animal products by adding natural substances to the feed that do not have adverse effects on the consumer, thus limiting the use of synthetic additives, with the ultimate goal of ensuring the balance between the animal, the producer, and the consumer-human as well as the entire ecosystem. This book is primarily addressed to the students of the Veterinary School of Aristotle University of Thessaloniki, as well as to undergraduate and postgraduate students who are taught the science of animal production, with the aim of conveying modern basic concepts and knowledge related to the Science of Animal Nutrition. Nevertheless, we believe it can also be useful to all those involved in the field of Nutrition. The content of the book is divided into five chapters. The first chapter refers to the composition of feeds and animal bodies, the second to the nutrients of feeds, the third to the digestion, absorption, and digestibility of the feed, the fourth to the energy of feeds and its importance in animal nutrition, and the fifth chapter to the additives in animal feeds. At the end, the relevant Greek and foreign language bibliography is provided, which constituted the main source of information for the writing of this book and to which the reader can refer for further information. (from the preface of the book)