In eukaryotic cells, repair of DNA double-strand breaks (DSBs) by the nonhomologous end-joining (NHEJ) pathway is critical for genomic stability. A functionally homologous repair apparatus, composed of Ku and a multifunctional DNA ligase (LigD), has recently been identified in many prokaryotes. Eukaryotic organisms employ a large number of factors to repair breaks by NHEJ. In contrast, the bacterial NHEJ complex is a two-component system that, despite its relative simplicity, possesses all of the break-recognition, end-processing, and ligation activities required to facilitate the complex task of DSB repair. Here, we review recent discoveries on the structure and function of the bacterial NHEJ repair apparatus. In particular, we discuss the evolutionary origins of this DSB repair pathway, how the diverse activities within the prokaryotic end-joining complex cooperate to facilitate DSB repair, the physiological roles of bacterial NHEJ, and finally, the essential function of NHEJ in the life cycle of mycobacteriophage.