Thymic epithelial tumors (TETs) are rare thoracic malignancies, with an overall incidence of 1.5 per million people. The TET Registry Project aims at federating an international network to provide a resource to support studies on the epidemiology and clinical management and monitoring some standards of clinical care of these tumors. Recorded data span all the specifications of the management of TET: paraneoplastic syndromes, histologic subtypes, diagnostic and staging issues, multimodal treatment strategies, and exceptional surgeries and therapies. Data collection for the registry is done both prospectively and retrospectively through different paths to allow the involvement of as many centers as possible, including data-sharing arrangements with some already established databases. This ambitious project implies the early setting of strong quality assurance measures looking at completeness, consistency, and accuracy of the data. These measures require a significant and long-term financial support that will also be free of possible sources of conflicts of interests.