This issue of Veterinary Clinics of North America: Small Animal Practice, edited by Elizabeth Stelow, focuses on Behavior as an Illness Indicator, with topics including: Best Practices in Diagnosing Behavior Problems and Developing Plans to Treat Behavior Problems; Separation, Confinement, or Noises; Managing Canine Aggression in the Home; Diagnosing and Treating Cats Who Urinate Outside the Box; Desensitization and Counterconditioning; Diagnosing Behavior Problems in Older Pets; Behavioral Nutraceuticals and Diets; and Advances in Behavioral Psychopharmacology.