The tumor, node and metastasis (TNM) classification for malignant tumors has been periodically revised in the International Union for Cancer Control (UICC) and American Joint Committee on Cancer (AJCC). As for lung cancer, the process of revision is quite unique compared with malignancies of other organs in that the corresponding professional society, the International Association for the Study of Lung Cancer (IASLC), has been playing a principal role in database construction, making revision agenda, simulation, and validation as a proposal to UICC and AJCC. The agenda articles have been already published for T, N, M, and stage grouping in the official journal of IASLC. In brief, the IASLC database included 77,156 evaluable patients diagnosed with lung cancer from 1999 to 2010, originating from 35 different databases in 16 countries of 5 continents. Among these, the data of 3905 patients were given by electric data capturing. In the T descriptors, new tumor-size groups were created: T1a </= 1cm; T1b >1-2 cm; T1c >2-3cm; T2a >3-4cm; T2b >4-5cm; T3 >5-7cm; and T4 >7cm. Endobronchial location <2cm from the carina has better prognosis than any other T3 descriptor and will be classified as T2. Total atelectasis/pneumonitis will be classified as T2 because it has a T2 prognosis. Diaphramatic invasion will be T4. Visceral pleural invasion remains the same, and mediastinal pleura invasion, seldom used, disappears as a T descriptor. The N component remains the same, but the number of involved nodal stations has prognostic impact. Therefore, it was proposed to divide N1 into N1a (single station N1) and N1b (multiple station N1), N2 into N2a1 (single station N2 without pN1 involvement), N2a2 (single station N2 with pN1 involvement) and N2b (multiple station N2) for testing. For the M component, M1a (intrathoracic metastases) remains the same, but extrathoracic metastases are divided into single extrathoracic metastasis (new M1b) and multiple extrathoracic metastases in a single or multiple organs (M1c). Regarding stages, stage IA is divided into IA1, IA2 and IA3 to accommodate T1a, T1b and T1cN0M0 tumors; all N1 disease are stage IIB except for T3-T4N1M0 that are IIIA; a new stage IIIC is created for T3-T4N3M0 tumors; and stage IV is divided into IVA (M1a and M1b) and IVB (M1c). The 8th edition of the TNM classification of lung cancer defines new tumor-size groups, confirms the prognostic relevance of quantifying nodal disease, establishes a new category for single extrathoracic metastasis, and creates new stage groupings. Looking at these, the importance of the accurate measurement of tumor diameter and accurate counting of the swollen nodes and lesions of distant disease has been raised. In this way it improves our understanding of the anatomic extent of the tumor, enhances, our capacity to indicate prognosis at clinical and pathologic staging, and increases the possibilities of research by facilitating tumor stratification for future clinical trials. Prognosis, TNM classification, Staging, lung cancer