This document provides information about pneumothorax, including its definition, mechanisms, pathophysiology, classification, clinical manifestations, diagnosis, and management. Pneumothorax is defined as the presence of air in the pleural space between the lung and chest wall. It can occur spontaneously due to lung blebs/bullae or underlying lung disease, or due to trauma. Management depends on the type and severity of pneumothorax, and may include observation, oxygen therapy, needle aspiration, chest tube drainage, chemical pleurodesis, or surgery. The goal is to promote lung re-expansion and prevent recurrence.