This chapter presents a state of the art summary of thymoma and thymic carcinoma (TC) to its biology, epidemiology, disease mechanisms, clinical signs, diagnosis, treatment and prognosis. TC, indeed, are morphologically similar to carcinomas arising in other sites and organs, and several variants are recognized, with squamous cell carcinoma being the most frequent subtype. TC is highly aggressive neoplasms; in addition to a local invasive tendency, they show an extrathoracic metastatic tendency toward the liver, bone marrow, and other sites. TC is tumors arising in the antero-superior mediastinum from the epithelial compartment of the thymus gland and is collectively also called "thymic epithelial tumors" (TET). A molecular classification of TET would contribute to identify prognostic as well as predictive biomarkers and to promote personalized treatment approaches. TET has lowest incidence in Northern and Eastern Europe, UK and Ireland, but somewhat higher incidence in Central and Southern Europe.