Tobacco smoking is the largest preventable risk factor for morbidity and mortality in industrialized countries. WHO estimates that tobacco will become the largest single health problem by 2020, causing an estimated 8.4 million deaths annually. Tobacco has central importance in the etiology of cancers of the lung, head and neck, urinary tract, and pancreas. Reducing the number of young people who take up smoking and helping those who have started to smoke to quit the habit are the key ways of preventing these cancers. Tobacco- or nicotine-dependence is a common, chronic, relapsing medical condition. Studies of twins have implicated genetic factors in most of the differences in vulnerability to tobacco smoke and in the persistence of the smoking phenotype. The available interventions for reducing tobacco use and treatment for nicotine dependence offer public health officials and clinicians the greatest single opportunity for disease prevention. Five medications -- nicotine chewing gum, nicotine patches, nicotine inhalers, nicotine nasal sprays and bupropion -- and behavioural therapy appear to be both effective and safe: they double the quitting rates and are associated with a dropout rate due to adverse events of less than 5%.