Lung cancer is one of the most common human cancers and the number one cancer killer in the United States. In general, lung cancer includes small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC), but NSCLC accounts for approximately 90% of lung cancer. The early diagnosis and therapy of lung cancer still presents a big challenge because validated screening tools, which can improve current early detection to reduce mortality from lung cancer, do not exist. Over the last decade, molecular genetic abnormalities have been described in NSCLC, including chromosomal aberrations, overexpression of oncogenes, and deletion and/or mutations in tumor suppressor genes. These molecular markers in NSCLC demonstrated close associations with the development of lung cancer such as Ras, the epidermal growth factor receptor (EGFR, or c-erbB-1), HER2 (c-erbB-2), c-Met, and Bcl-2. Therefore, this information may be applied for early cancer detection, classification, novel targeted therapy, and prognosis in NSCLC. Recent clinical data have revealed that targeted therapy might be the second-line therapy as an alteative approach. Currently, the targeted therapies are mainly focused on two lung cancer pathways, the EGFR and the vascular endothelial growth factor (VEGF) pathways. Some clinical trials are very encouraging, but some of them are not. However, these trials have not identified a subgroup of NSCLC with biomarkers. Therefore, it is very important to select NSCLC patients with biomarkers to match targeted agents so that we can further identify effectiveness of targeted therapy in the future.