The authors present an overview of thirdhand smoke (THS) in the U.S. and presents arguments on why it should be considered in the development of smoke-free policies to reduce tobacco-related morbidity. Topics include how THS residue is formed, concerns regarding THS in terms of its ability to form new toxicants and carcinogens such as carcinogenic tobacco-specific nitrosamines (TSNAs), and suggestions for research on the harmful effects of THS exposure and its reduction.