The first step of the treatment of lung cancer is the definition of the stage of the disease. International Association for the Study of Lung Cancer (IASCL) established the new lung cancer staging project, because there were many problems with the 1997 international staging system. In this article, we summarized the recommendations of International Staging Committee which was established by IASCL for the definitions for the tumor, node, metastasis (TNM) descriptors and the staging groups in the new lung cancer staging system, which have been accepted by the Union Internationale Contre le Cancer (UICC) and the American Joint Committee on Cancer (AJCC). (Tur Toraks Der 2010; 11: 173-80)