Asthma is a severe and growing threat affecting both children and adults in both developing and developed world, currently affecting approximately 8% of US population. It is becoming increasingly recognized as a syndrome constituted by airway obstruction, airway hyperresponsiveness, and airway inflammation with different causes, associated risk factors, and underlying pathophysiology. The advances in basic and clinical research of asthma have accelerated over the past 20 years with increasing diagnostic tools, especially biomarkers, that led to specific characterization of individual patient's asthma pathophysiology, or disease "phenotype" and "endotype," which allowed precision medicine therapies, including new asthma biologics. This book aims to update the paradigm shifts in precision medicine of asthma diagnosis and management, driven by underlying phenotypes or endotypes.