Since the previous edition of this text was published there has been a sustained expansion in the knowledge and understanding of the pathophysiology of the medical diseases that affect the dog. This has been complemented by significantly improved methods to diagnose and manage these diseases. The fourth edition of this textbook has been designed to reflect these many advances and has necessitated a radically different approach from the previous edition. There are now fourteen sections, each with an editor to co-ordinate the chapters in that section. The number of authors contributing to this edition has expanded from twenty-nine to seventy-eight. Each section in the book has been written to give both concise reviews of the subject and a logical approach to the management of the clinical problems. A significant number of tables, flow diagrams and illustrations have been included to assist the clinician in accessing key clinical information.