Biomarkers relevant to lung cancer can be classified into three broad categories: serum markers, tissue markers, and sputum markers. The predominant contribution of serum biomarkers will be in documenting disseminated disease and response to therapy. The most promising role for tissue biomarkers, at least in non-small cell lung cancer, is for the determination of prognosis in resectable patients. Sputum biomarkers offer considerable promise as early detection tools, which may enhance the sensitivity and specificity of screening when used in conjunction with periodic screening chest radiographs.