Pneumothorax is the presence of air in the pleural space and can occur spontaneously or due to injury. It is classified as primary, occurring without lung disease, or secondary, occurring in patients with lung diseases like COPD. Symptoms include chest pain and breathlessness. Examination may find decreased or absent breath sounds on the affected side. Chest x-ray shows the lung edge and any mediastinal shift. Small, asymptomatic primary pneumothoraces may resolve on their own, while chest tubes and observation are usually needed for secondary cases. Recurrent cases often require pleurodesis surgery to prevent future occurrences.