Lung cancer occurs through a complex multistage process that results from the combination of carcinogen exposure and genetic susceptibilities. The primary etiology of lung cancer is tobacco smoking, but an understanding of why some smokers develop lung cancer, and others do not, remains unclear. Current studies focus on genetic susceptibilities to lung cancer, and how they modify the effects of tobacco smoke carcinogens. New assays are being developed to study other contributors to cancer risk, such as interindividual differences in DNA repair. There is current evidence to suggest that the risk of lung cancer for women, compared to men, is higher for the same level of smoking. Several biological differences for the types of lung cancer have been observed in women and men. Also, there appear to be differences in lung cancer between Caucasians and African-Americans. Molecular epidemiology tools are uniquely suited to study these biological differences. These studies will improve cancer risk assessments and focus cancer prevention strategies. Other studies also are focusing on tobacco addiction, in order to lead to improved smoking cessation strategies.