All cancer cells possess defects in DNA repair mechanisms. Poly(ADP-ribose) polymerase 1 (PARP1) plays an important role in DNA repair, with recruitment of PARP1 one of the earliest events in the DNA damage repair response. Inhibition of PARP1 has considerable therapeutic potential in the treatment of various cancers, including ovarian cancer, breast cancer, prostate cancer and non-small cell lung cancer. The predominant mechanism of action of the PARP inhibitors is synthetic lethality, whereby two pathway defects have limited effect separately, but when both are present in the cell become lethal. This synthetic lethality has rendered the PARP1 inhibitors particularly useful in tumors with BRCA1 or BRCA2 loss-of-function mutations. Identification of other biomarkers that may help select for patients for whom PARP inhibitors are likely to be useful remains a significant challenge. This collection of recent high-quality full-text articles from Springer Nature and other prominent publishers provides an overview of the role of PARP1 in DNA repair and the use (and potential) of PARP inhibitors in cancer treatment.