This article reviews studies of the effect of tobacco control policies on smoking rates with the aim of providing guidance on the importance of different policies. Based on past studies, we estimate the magnitude of effects of major tobacco control policies, how their effects depend on the manner in which the policies are implemented, the relationship between the different policies, and the barriers to implementation. The most successful campaigns have implemented a combination of tobacco control policies. Of those policies, substantial evidence indicates that higher taxes and clean air laws can have a large impact on smoking rates. Evidence also indicates that media campaigns when implemented with other policies are important. Research on greater access to treatment and telephone support hotlines indicates a strong potential to increase quit rates and may be important in affecting heavier smokers. Direct evidence on the effects of advertising bans and health warnings is mixed, but these policies appear to be important in some of the countries that have had success in reducing smoking rates. School education programs and limits on retail sales are not likely to have much impact if implemented alone, but may be more important when combined with other policies.