A pneumothorax is defined as a collection of air outside the lung but within the pleural cavity. It occurs when air accumulates between the parietal and visceral pleurae inside the chest. The air accumulation can apply pressure on the lung and make it collapse. The degree of collapse determines the clinical presentation of pneumothorax. Air can enter the pleural space by two mechanisms, either by trauma causing a communication through the chest wall or from the lung by rupture of visceral pleura. There are two types of pneumothorax: traumatic and atraumatic. The two subtypes of atraumatic pneumothorax are primary and secondary. A primary spontaneous pneumothorax (PSP) occurs automatically without a known eliciting event, while a secondary spontaneous pneumothorax (SSP) occurs subsequent to an underlying pulmonary disease. A traumatic pneumothorax can be the result of blunt or penetrating trauma. Pneumothoraces can be even further classified as simple, tension, or open. A simple pneumothorax does not shift the mediastinal structures, as does a tension pneumothorax. Open pneumothorax is an open wound in the chest wall through which air moves in and out.