Having a clear understanding of the divisions of the mediastinum is important for the thoracic surgeon who daily has to establish a differential diagnosis of mediastinal masses based on their location, as well as to select the best surgical approach to access the mediastinum to obtain diagnostic material, to drain mediastinal spaces, or to excise mediastinal tumors. In this respect, the most useful classifications appear to be the 3-compartment model and Shields' 3-zone classification. This article describes the various classifications of the mediastinum.