Airway smooth muscle is fundamental for maintaining airway tone. The specialized ultrastructural features and regulatory mechanisms of airway smooth muscle are vital for normal airway function. Previous studies have shown that airway smooth muscle undergoes phenotypic changes during development and in various respiratory disorders. Airway smooth muscle may also mediate the immune response by secreting cytokines and chemokines. Cultured tracheal smooth muscle cells (TSMC) express three p21-activated kinase (PAK) isoforms which may promote TSMC migration by signaling to p38 MAPK. Human Tracheal Smooth Muscle Cells proliferation is an important component of airway remodeling in asthma. It is consequently a target for the development of novel anti-asthma agents.