Although the overall prevalence of tobacco smoking in the United States is decreasing, the proportion of light smokers is increasing and is as high as 50% among some groups. There is growing evidence that light smokers experience significantly higher health risks compared to nonsmokers, and they are often unable to quit smoking on their own. The prevalence of light smoking differs among subpopulations in the US and is particularly common among adolescents, college students, pregnant women, and some ethnic minorities. Characteristics of light smokers in these subpopulations vary, as do the underlying reasons for smoking, barriers to cessation, and treatment issues. Unfortunately, the paucity of research to develop and test effective cessation aids is common across all groups of light smokers. Given the substantial portion of light smokers in these populations, development and dissemination of effective behavioral and pharmacological interventions for light smokers is likely to result in substantial smoking reduction rates in the general population.