This book elucidates the diagnostic criteria and concept of asthma-COPD overlap (ACO) and provides the latest information on its epidemiology, pathophysiology, diagnostic criteria, and treatment options. It discusses the controversy-causing findings of prognosis of ACO, the novel molecular mechanism including nitrosative stress, radiological or physiological features, findings by research that used HRCT or forced oscillation technique. In addition to a recent animal model of ACO, the role of each biomarker, the latest results of ICS/LAMA/LABA combination inhalers or biologics is also debated. Asthma COPD Overlap -Updated Concept, Pathophysiology, Diagnosis, and Treatment is addressed not only to beginners, but also to physicians engaged in clinical practice, supervisors, and many basic researchers. Covering every aspect of ACO, it serves readers to improve diagnosis or treatment for patients with ACO.