The tracheobronchial tree begins to form during the fourth week of development through a series of dichotomic divisions of an entoblastic evagination. The morphogenesis and maturation of the respiratory tract depend both on the nature of the extracellular matrix which facilitates cell migration and on epithelial-mesenchymal interactions which induce the proliferation and differentiation of epithelial cells. The study of the plasticity and the phenotypic modifications of secretory cells during both development and inflammatory remodeling of the tracheobronchial mucosa suggests an important role for secretory cells during ciliogenesis and repair.