Thirdhand smoke (THS) is defined as residual tobacco components that remain on indoor surfaces after tobacco has been smoked, such as walls furniture, and dust particles, which are re-emitted into the air. THS also includes secondary pollutants generated from the reaction of surface residual smoke compounds with reactive indoor air pollutants. THS is a new hidden health hazard, with infants and children being most at risk of higher exposure. This article summarized the aging process of secondhand smoke and the mechanism of generation of THS; reviewed the current status of research on THS regarding its chemical constituents, physical and chemical properties, biological toxicity, as well as degree of pollution in China and other countries; and finally provided the perspectives on the future study of THS.