Small airways play a pivotal role in the early pathological changes of various lung diseases, including asthma, chronic obstructive pulmonary disease, and interstitial lung disease. Owing to the large cross-sectional area of small airways, conventional spirometry may not be sensitive enough, leading to the potential neglect of small airway dysfunction. This article, drawing on the latest findings and academic perspectives in related research fields, briefly introduces the anatomical structure, pathophysiological characteristics, functional measurements, and clinical significance of small airways. The aim is to facilitate early diagnosis, risk prediction, and precision treatment of small airway dysfunction associated with chronic obstructive pulmonary disease and asthma.