A double-lumen tube (DLT) is an endotracheal tube designed to isolate the lungs anatomically and physiologically. Double-lumen tubes (DLTs) are the most commonly used tubes to provide independent ventilation for each lung. One-lung ventilation (OLV) or lung isolation is the mechanical and functional separation of the 2 lungs to allow selective ventilation of only one lung. The other lung that is not being ventilated passively deflates or is displaced by the surgeon to facilitate surgical exposure for non-cardiac operations in the chest such as thoracic, esophageal, aortic and spine procedures. This activity reviews the use of the DLT, its indications, contraindications, and complications in thoracic surgery.