The bronchi are airway passages that conduct air from the trachea to the lungs. The bronchi branch and form the bronchial tree. The first two bronchi arising from the trachea are the right and left main (or principal) bronchi.

Each main bronchus divides into lobar bronchi. Each lobar bronchus divides into segmental bronchi, which further divide into intrasegmental bronchi. Finally, the smallest bronchi divide into bronchioles. Each bronchiole divides into smaller bronchioles within the lungs until the terminal bronchiole.

The terminal bronchioles give rise to respiratory bronchioles that divide further into alveolar ducts. Alveolar ducts lead to alveoli forming the alveolar tree within the lungs.