The genetic diversity comprised in farm animal species and breeds is an important resource in livestock systems. For several reasons, within the different species used for food production, only a few breeds are developed towards high-output breeds fitting in high-input systems. In this process many breeds are set aside from the food producing livestock systems. These breeds will be faced with extinction unless new functions for these breeds are found. This is a real threat for the genetic diversity within species. This book is intended to give insight into the issues of the utilisation and conservation of farm animal genetic resources towards a broad group of readers interested in these subjects. The insight is presented as applications of population, molecular and quantitative genetics that can be used to take appropriate decisions in utilisation and conservation programmes. A previous edition of this book is a key resource in courses worldwide and cited in many scientific publications. The first two chapters discuss the decisions to be made in utilisation and conservation. Chapter 3 surveys the different ways in which the diversity we observe within a species can be characterised. Chapter 4 illustrates recent results using this theory for utilisation and conservation purposes. Chapters 5, 6 and 7 give theoretical backgrounds necessary to make decisions and chapters 8 and 9 present the operation and practical implications of selection and conservation schemes.