Mediastinal interfaces on a chest radiograph result from contact between mediastinal structures and the adjacent lung, while mediastinal lines result from contact between the two lungs across the midline. A variation of mediastinal interface is mediastinal stripe, a narrow band produced by contact of both sides of a mediastinal structure with the lungs. Alterations in mediastinal interfaces and lines may be due to variations in normal anatomy, or may reflect the presence of abnormalities within the mediastinum. Familiarity with the various normal mediastinal interfaces and lines, and the changes that occur with disease is important for the interpretation of the chest radiograph and in the diagnosis of mediastinal abnormalities. The purpose of this pictorial essay is to illustrate the most important normal and abnormal interfaces and lines and also to correlate radiographic and CT findings.