In 2001, a systematic review for the Guide to Community Preventive Services identified strong evidence of effectiveness of smoking bans and restrictions in reducing exposure to environmental (secondhand) tobacco smoke. As follow-up to that earlier review, the focus here was on the evidence on effectiveness of smokefree policies in reducing tobacco use. Smokefree policies implemented by worksites or communities prohibit smoking in workplaces and designated public areas. The conceptual approach was modified for this review; an updated search for evidence was conducted; and the available evidence was evaluated. Published articles that met quality criteria and evaluated changes in tobacco-use prevalence or cessation were included in the review. A total of 57 studies were identified in the period 1976 through June 2005 that met criteria to be candidates for review; of these, 37 met study design and quality of execution criteria to qualify for final assessment. Twenty-one studies measured absolute differences in tobacco-use prevalence with a median effect of -3.4 percentage points (interquartile interval: -6.3 to -1.4 percentage points). Eleven studies measured differences in tobacco-use cessation among tobacco users exposed to a smokefree policy compared with tobacco users not exposed to a smokefree policy. The median absolute change was an increase in cessation of 6.4 percentage points (interquartile interval: 1.3 to 7.9 percentage points). The qualifying studies provided sufficient evidence that smokefree policies reduce tobacco use among workers when implemented in worksites or by communities. Finally, a systematic economic review identified four studies that, overall, demonstrated economic benefits from a smokefree workplace policy. Additional research is needed to more fully evaluate the total economic effects of these policies.