The identification of lung sliding rules out the presence of pneumothorax with 100% certainty in the area being scanned (Discussion Video Set, Video 1). Lung sliding was originally described in 1995 by Lichtenstein and Menu as an “interface between the soft tissues of the chest wall and aerated lung.” Lung sliding is appreciated as movement at the pleural line with respiration and can be assessed at any point on the chest wall. If lung sliding is present, there is direct apposition between the parietal and visceral pleurae, excluding the presence of a pneumothorax. It is therefore essential to identify and establish the presence of lung sliding prior to any thoracic procedures. The absence of lung sliding (Discussion Video Set, Video 2) raises the possibility of a pneumothorax but can also be seen in other conditions that may cause the adherence of the visceral and parietal pleurae (such as in ARDS), complete atelectasis (as in right mainstem intubation), or iatrogenic pleurodesis (as in patients with treated malignant pleural effusions). In these situations, other sonographic findings can help to rule out a pneumothorax. These findings include lung pulse and “B” lines. Lung pulse represents transmitted cardiac pulsation appreciated at the pleural line when visceral and parietal pleurae are opposed (Discussion Video Set, Video 4). B lines represent vertical reflection artifacts consistent with alveolar-interstitial syndromes, as the source of B lines is within the lung parenchyma, and their presence rules out intrapleural air. Absence of lung sliding with the presence of lung point (Discussion Video Set, Video 3) verifies the presence of a pneumothorax. Lung point represents the interface between the pneumothorax and the aerated lung. During inspiration, the collapsed lung may expand to reach the chest wall, allowing visualization of lung sliding intermittently, until expiration, when the lung is once again removed from the chest wall. Both low- and high-frequency transducers have the ability to visualize the pleural line, and there have been no studies comparing which transducer is better for the diagnosis of a pneumothorax. The high-frequency transducer allows closer inspection of the pleural line and is frequently used when ambiguity exists regarding lung sliding or lung pulse.