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 usually in young, tall smokers, or secondary, affecting those with lung diseases like COPD. Symptoms include chest pain and breathlessness. Examination may find reduced 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 without treatment while larger ones often require chest tube drainage. Surgery is recommended after recurrent episodes to prevent future occurrences.