Asthma and chronic obstructive pulmonary disease (COPD) are prevalent obstructive lung diseases, both of which are characterized by airflow limitation. Although both represent distinct pathogenic entities, there can be significant clinical and physiologic overlap between the 2 disorders, creating potential management difficulties for clinicians. Although practice guidelines for both conditions outline diagnostic and management strategies, asthma and COPD are highly heterogeneous, and the symptoms of many patients remain poorly controlled despite adherence to current guidelines. Recent advances in phenotyping studies have elucidated heterogeneity in these airway diseases and might represent the best opportunity to enhance diagnosis, predict outcomes, and personalize treatments in patients with asthma and those with COPD. This review will focus on recent advances in describing phenotypic heterogeneity in asthma and COPD, including the evaluation of multiple clinical variables, molecular biomarkers, physiologic and radiologic data, and factors associated with disease progression and frequent exacerbations.