The last two decades have seen the maturation of the field, which has broadened its focus from PARP1 and bacterial toxins to various PARP proteins and other ADP-ribosylation “writers,” “erasers,” and “readers.” ADP-ribosylation also proved its therapeutic relevance, particularly with the two seminal studies in 2005 that reported synthetic lethality between inhibition of PARP1 or PARP2 and BRCA (breast cancer gene) deficiency,3,4 paving the way for the current widespread use of PARP inhibitors (PARPi) in treating specific cancer types. The gene discussed is PARP1; the disease is cancer.