Breathing secondhand smoke (SHS) causes heart disease and lung cancer in adults and increased risks for sudden infant death syndrome, acute respiratory infections, middle-ear disease, worsened asthma, respiratory symptoms, and slowed lung growth in children. No risk-free level of exposure to SHS exists. The Global Youth Tobacco Survey (GYTS), initiated in 1999 by the World Health Organization (WHO), the Canadian Public Health Association, and CDC includes questions related to tobacco use, including exposure to SHS. This report examines data collected from 137 jurisdictions (i.e., countries and territories) during 2000-2007, presents estimates of exposure to SHS at home and in places other than the home among students aged 13-15 years who had never smoked, and examines the association between exposure to SHS and susceptibility to initiating smoking. GYTS data indicated that nearly half of never smokers were exposed to SHS at home (46.8%), and a similar percentage were exposed in places other than the home (47.8%). Never smokers exposed to SHS at home were 1.4-2.1 times more likely to be susceptible to initiating smoking than those not exposed. Students exposed to SHS in places other than the home were 1.3-1.8 times more likely to be susceptible to initiating smoking than those not exposed. As part of their comprehensive tobacco-control programs, countries should take measures to create smoke-free environments in all indoor public places and workplaces.