Third-hand smoke (THS) is the residual tobacco smoke contaminant that remains after a cigarette is extinguished. It can react with the indoor air pollutant nitrous acid to produce a carcinogen. Understanding perceptions of THS is critical, as it may inform the development of messages for promoting smoke-free homes. Six focus groups, of smokers and non-smokers, with 39 participants were conducted. Participants were asked whether they knew about THS and its harmful effects and whether it would motivate people to make their homes smoke free. They also answered questions about THS beliefs. Participants were mostly African-American, female and high-school graduate or General Educational Development (GED) recipients. Most of the participants had not heard about it and did not know what THS was. When asked about the dangers of THS, some participants made references to children indicating that they can easily inhale or ingest the residue leading to harmful effects. Almost all of the participants stated that they thought being educated about THS would motivate people to make their homes smoke free. There is a need for more scientific understanding of the potential dangers of THS and subsequent education about its exposure and harm to children and possibly adults.