Translesion replication is a mechanism that employs specialized DNA polymerases for promoting continued nascent strand extension at forks blocked by the presence of unrepaired DNA damage. In Saccharomyces cerevisiae at least, this process contributes only modestly to the ability of cells to tolerate DNA damage, but is a major source of DNA-damage-induced substitutions and frameshifts, and of spontaneous mutations. Translesion replication past many types of DNA damage in yeast depends on the activities of DNA polymerase zeta (pol zeta) and Rev1p. Pol zeta is found in most, but not all, eukaryotes investigated, whereas Rev1p appears to be universal. Genes encoding these enzymes are found in humans, and appear to perform functions similar to those in yeast.