The mediastinum is located in the central portion of the thorax and is defined as the space between the two pleural cavities bounded anteriorly by the sternum, posteriorly by the vertebral column, superiorly by the thoracic inlet and inferiorly by the diaphragm. Mediastinum is divided into anterior, middle and posterior for anatomic and surgical convenience. The anterior compartment is limited anteriorly by the sternum, and posteriorly by the anterior margin of the pericardium, aorta and brachiocephalic veins. The posterior compartment is bounded anteriorly by the posterior margins of the pericardium and great vessels and posteriorly by the thoracic vertebral bodies. The middle compartment is defined by the margins of the anterior and posterior compartments. Each compartment has specific components and hence its specific disease. Chest radiograph with CT is recommended as the primary imaging modality for assessing masses precise localisation of the mass. Anterosuperior compartment lesions predominate in adults while seen while posterior compartment lesions predominate in children. The four most common anterior mediastinal tumors are thymomas, teratomas, lymphomas, and enlarged or ectopic thyroid tissues are often referred to as the “4 T\'s” (Thymoma, Teratoma, Terrible lymphoma, and Thyroid). Congenital cysts, aneurysm and lymphadenopathy form common middle mediastinal lesions whereas neurogenic and esophageal lesions form common posterior mediastinal lesions. Pneumomediastinum (mediastinal emphysema) a condition affecting the mediastinum caused due to air or gas outside the normal confines of the respiratory or gastrointestinal tract is also discussed.