This chapter is written in the question and answer format, which gives the description on the respiratory system. Respiratory system is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. This chapter covers the basic approach, symptomatology and investigations, bronchial asthma, chronic obstructive pulmonary disease (COPD), mycobacteria, tuberculosis, antituberculous drugs (ATDs), extra-pulmonary tuberculosis (EPTB), suppurative lung disease, pleural effusion, pneumothorax, pneumonia, diffuse parenchymal lung disease, occupational lung diseases, lung cancer (bronchial carcinoma), respiratory failure, sleep apnea or hypopnea syndrome, hemoptysis, dyspnea, and pulmonary eosinophilic syndromes. Asthma is a chronic inflammatory disorder of the airways (bronchial tree) in which breathing is periodically rendered difficult by widespread narrowing of the bronchi (reversible bronchoconstriction). EPTB constitutes 15 to 20% of all cases of TB immunocompetent patients and in HIV positive patients, EPTB accounts for more than 50% of all cases of TB. Heterogenous group of pulmonary disorder is characterized by pulmonary parenchymal or peripheral blood eosinophilia.