In this issue of Veterinary Clinics of North America: Equine Practice, guest editor Dr. Lais R. R. Costa brings her considerable expertise to the topic of A Problem-Oriented Approach to Immunodeficiencies and Immune-Mediated Conditions in Horses. Top experts in the field focus on a problem-oriented approach, starting with the clinical presentation, differential diagnosis, and tools to rule out other conditions to reach the final diagnosis of the immunologic condition, followed by discussion of pathogenesis, management, and treatment.