Tanslesion DNA synthesis (TLS) is one mode of DNA damage tolerance in cells upon genotoxic agent treatments, which utilizes specialized low-fidelity DNA polymerases to traverse replication-blocking lesions. TLS can be classified into two categories: error-prone TLS and error-free TLS. Error-prone TLS is one of the fundamental mechanisms for genome mutagenesis. In addition, recent studies suggest that TLS is closely related to tumor chemoresistance. So far, multiple TLS polymerases have been identified. The known major TLS polymerases belong to Y-family DNA polymerases, which include Polκ. The general properties of TLS and the current understanding of Polκ in mammals were summarized.