The repair of DNA double-strand breaks by non-homologous end-joining (NHEJ) has long been thought to be restricted to eukaryotes. However, recent papers document the existence of operons encoding functional NHEJ complexes in some bacteria. These findings provide new evolutionary insights into the core biochemistry of this repair pathway, and suggest that one function driving the selection of NHEJ in bacteria, and perhaps eukaryotes, relates to prolonged periods of mitotic exit.