Extrapulmonary air can occur in various clinical conditions including both thoracic and non-thoracic pathologies. Thoracic pathologies certainly represent the vast majority, but extrapulmonary air can also derive from affections of the neck or abdomen. Anatomically, there are no barriers in the subcutaneous tissue or in the perivertebral space, allowing air to move freely. The visceral and retropharyngeal cervical spaces indeed connect with the mediastinum and the thoracic cavity links to the abdomen through the diaphragmatic hiatus. Abnormal air in the thoracic cavity can collect in multiple spaces, including the pleural cavity, chest wall, mediastinum, and pericardium. Thus one of the most recognized classifications of extrapulmonary air is based on the localization: mediastinal, pericardial, pleural, or chest wall. In this chapter, all of these conditions will be reviewed, as well as the related CT findings that need to be described in the report, in addition to those of the determining conditions.