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. Diagnosis is made through chest x-ray showing lung edge and lack of markings between lung and chest wall. Small primary pneumothorax may resolve on its own but others require chest tube placement and hospital monitoring. Recurrent spontaneous pneumothorax requires pleurodesis surgery after second occurrence to prevent future episodes.