The phenomenon of sodium hunger was discovered by Curt Richter, the great American psychobiologist, over fifty years ago, and has since been the source of intense study by naturalists, psychologists, endocrinologists, physiologists, and neuroscientists. In this account, Professor Schulkin uses hunger for sodium as a model system in which to study how the brain produces motivated behavior. He offers a systematic account of the behavior of the sodium hungry animal and explores the endocrinological and physiological mechanisms that maintain sodium balance and then act on the brain to promote the search for and the ingestion of salt. Finally, the book provides a description of a neural network that orchestrates the behavior of salt seeking and salt ingestion.