An encyclopedia should properly encompass the totality of human knowledge, or at least of some particular sector of it. The subject matter of animal science is largely covered in this book. Its aims are completeness, accuracy, succinctness and ease of access. To encompass the whole of encyclopedia in this space obviously several efforts have been made. Finally, ease of access is ensured by the alphabetical arrangement of the entries. There is more on this in the note that follows. Although there have been other encyclopedias of animal science they have been more in the nature of collections of review articles, valuable certainly, but not providing the ready access to specific facts and figures that is the essence of this work. This is the first encyclopedia to be devoted exclusively to the animal science, including birds and fish. It contains around 2000 entries. The entries range from short definitions of terms to extended descriptions of subjects of major importance. The encyclopedia includes definitions of terms commonly used in animal science; chemistry and functions of nutrients, important metabolites, toxins, etc.; explanations of nutritional processes; their physiological and metabolic bases; descriptions of the major farmed species, their metabolism and practical feeding; composition and nutritional value of important crops and feedstuffs; feed processing; feeding systems. It is intended as a book that users will regularly refer to for information because they know it will be there. Because this is the first time that such an encyclopedia has been published, it must also be seen as a work in evolution, not yet complete.