ADP-ribosylation is the post translational modification of proteins catalyzed by ADP-ribosyltransferases (ARTs). ADP-ribosylation has been implicated in a wide variety of cellular processes, including cell growth and differentiation, apoptosis and transcriptional regulation. Perhaps the best-characterized role, however, is in DNA repair and genome stability, where ADP-ribosylation promotes resolution of DNA single-strand breaks. Although ADP-ribosylation also occurs at DNA double-strand breaks (DSBs), which ARTs catalyze this reaction and the molecular basis of how this modification regulates their repair remains a matter of debate. Here, we review recent advances in our understanding of how ADP-ribosylation regulates DSB repair. Specifically, we highlight studies using the genetic model organism Dictyostelium in addition to vertebrate cells that identify a third ART that accelerates DSB repair by non-homologous end joining through promoting the interaction of repair factors with DNA lesions. The implications of these data with regards to how ADP-ribosylation regulates DNA repair and genome stability are discussed.