The mediastinum is composed of various structures within the central portion of the thorax that are bounded by the lungs, the diaphragm, and the thoracic inlet. Because of this wide variety of anatomic structures, mediastinal tumors constitute a heterogeneous group of neoplasms, both primary and metastatic. Detection of mediastinal abnormalities requires familiarity with the chest radiograph, as most mediastinal tumors are discovered in asymptomatic patients on routine chest radiography. Once a mediastinal abnormality is detected by a chest radiograph, further radiologic evaluation involves cross-sectional imaging with computed tomography (CT) or magnetic resonance imaging (MRI) and may employ other imaging techniques, such as positron emission tomography (PET) or integrated PET/CT. This article will review fundamental radiologic findings of mediastinal abnormalities on chest radiographs and will address the salient features of mediastinal tumors on other imaging modalities, including CT, MRI, PET, and integrated PET/CT.