This chapter focuses on the anatomy of the respiratory system and the disorders of the respiratory system. The normal adult right lung weighs 375 to 550 gm (average 450 gm) and is divided by two fissures into three lobes—the upper, middle and lower lobes. The airways of the lungs arise from the trachea by its division into right and left main bronchi which continue to divide and subdivide further, eventually terminating into the alveolar sacs. The bronchi and their subdivisions up to bronchioles are lined by pseudo-stratified columnar ciliated epithelial cells, also called respiratory epithelium. Developmental defects involving deficiency of bronchial or bronchiolar cartilage, elastic tissue and muscle result in congenital cystic disease of lungs. Sequestration is the presence of lobes or segments of lung tissue which are not connected to the airway system. Acute respiratory distress syndrome (ARDS) is a severe form of progressive respiratory insufficiency which involves pulmonary tissues diffusely i. e. involvement of the alveolar epithelium, alveolar lumina and interstitial tissue. Pneumonia is defined as acute inflammation of the lung parenchyma distal to the terminal bronchioles.