The twentieth century may be looked back upon as the century of lung cancer. At the beginning of the century lung cancer was quite rare, but this century the rates have increased approximately 10-fold and it is the second most common type of cancer and has become the leading cause of death due to cancer in the United States. The rate of lung cancer among U.S. women continues to rise, in contrast rates in U.S. men have been declining since about 1990. Cigarette smoking accounts for 85-90% of lung cancer deaths in the United States. However, only 10-15% of smokers eventually develop lung cancer. In the past 25 years, since the U.S. Surgeon General's ground breaking report in 1964, overall smoking rates have been declining, but smoking still remains a significant behavior. More troubling, the rates of smoking continue to increase in many parts of the world. Advances in molecular biology and early diagnosis have increased the understanding of lung cancer etiology and may be effective in uncovering more efficient detection and treatment regimens. These advances will hopefully make lung cancer as uncommon at the end of the twenty-first century, as it was at the beginning of the twentieth century.