This chapter discusses the respiratory system, focusing on the chest X-ray and its interpretation. It highlights physical signs and radiological appearances of respiratory diseases, including consolidation, pleural effusion, and lung collapse. The text also covers hypoxia, defined as inadequate tissue oxygenation, and its classification based on factors affecting tissue oxygen delivery. Respiratory failure is categorized into types I, II, III, and IV, each with specific clinical presentations and management strategies. Noninvasive monitoring techniques such as pulse oximetry and capnography are discussed, along with methods of oxygen delivery and mechanical ventilation. The chapter also addresses complications of ventilatory support, modes of ventilatory support, and liberation from mechanical ventilation. Additionally, it covers specific conditions like acute hypoxemic respiratory failure, community-acquired pneumonia, health-care-associated pneumonia, pulmonary tuberculosis, aspiration syndromes, acute severe asthma, and pulmonary embolism, providing detailed clinical features, diagnosis, and management strategies.This chapter discusses the respiratory system, focusing on the chest X-ray and its interpretation. It highlights physical signs and radiological appearances of respiratory diseases, including consolidation, pleural effusion, and lung collapse. The text also covers hypoxia, defined as inadequate tissue oxygenation, and its classification based on factors affecting tissue oxygen delivery. Respiratory failure is categorized into types I, II, III, and IV, each with specific clinical presentations and management strategies. Noninvasive monitoring techniques such as pulse oximetry and capnography are discussed, along with methods of oxygen delivery and mechanical ventilation. The chapter also addresses complications of ventilatory support, modes of ventilatory support, and liberation from mechanical ventilation. Additionally, it covers specific conditions like acute hypoxemic respiratory failure, community-acquired pneumonia, health-care-associated pneumonia, pulmonary tuberculosis, aspiration syndromes, acute severe asthma, and pulmonary embolism, providing detailed clinical features, diagnosis, and management strategies.