Weaning represents a significant challenge to every young piglet and the success of the process is crucial to the lifetime performance of the animal. The transition from a liquid diet to one that is usually based on dry good ingredients is accompanied by major changes in digestive physiology, immune status and social and physical environments. Successful weaning is, therefore, thekey to effective growth, feed efficiency and the subsequent development of the pig. The book is developed from a British Society of Animal Science occasional meeting, held in September 2000. It brings together all of the scientific disciplines involved in the pre and post-weaning biology/development, nutrition, immunology/health, ethology and the physical environment.