The International Association for the Study of Lung Cancer (IASLC) Staging Project is a global effort to study and improve the current staging system for lung cancer, mesothelioma, thymic tumors, and esophageal cancer. The IASLC Staging Manual in Thoracic Oncology, 3rd Edition describes the cumulative findings of the third phase of the IALSC Staging Project. The revised tumor, node, metastasis (TNM) classification system described in the Manual informs the 9th edition staging system for the American Joint Committee on Cancer and the Union for International Cancer Control.