Staging classification of lung cancer according to the anatomic TNM (T-primary tumor, N-regional lymph nodes, M-distant metastasis) system has served the scientific community well since its introduction over 50 years ago. Refinements in the TNM definitions and stage grouping rules reflect the dynamics of new knowledge and experience gained from wide application of the staging concept. The present International System for Staging Lung Cancer provides the means for consistent, reproducible classification that enables universal communication throughout the world regarding the status of treatment for lung cancer; however, investigation of the prognostic implications of various staging factors is warranted. The challenge for the future lies in incorporating biological marker information into a prognostic index.