Smoking is one of the most harmful habits, and the leading cause of cancer of respiratory organs, and many others. Tobacco smoke consists of approximately 4.700 of chemical compounds which include about 50 carcinogenic. The complexity of cigarette smoke causes confusion in the literature about the mechanisms by which carcinogens induce cancer development. While some authors simplify mechanisms, referring to the smoke just as tar or implying only one component (B[a]P-7,8-diol-9,10-epoxide), others believe that the mechanisms are still unknown. This paper presents a brief overview of the most important tobacco-related carcinogens, and the manner in which they react with DNA and cause genetic changes (mutations) in oncogens and tumor suppressor genes. Emphasis is thereby placed on the polycyclic aromatic hydrocarbons, nitrosamines and aromatic amines that forming DNA adducts as the most important biomarkers in determining the carcinogenic effects of compounds in cigarette smoke. Tobacco smoke also contains large amount of inorganic carcinogens such as metals and free radicals that have a twofold effect in carcinogenesis, reacting directly with DNA or indirectly through other compounds. The most important non-carcinogen in smoke is nicotine. This compound is addictive and person continues to smoke despite the adverse health consequences. For this reason, nicotine is the main "culprit" as smoking has become a major cause of cancer, ie 30% of all deaths caused by cancer is associated with the consumption of tobacco products.