Poly(ADP-ribose) polymerase (PARP) catalyzes the biochemical conversion of nicotinamide adenine dinucleotide (NAD+) to poly(ADP-ribose) and nicotinamide, which is a weak feedback inhibitor of the enzyme. Early designs of PARP inhibitors were primarily based on mimicking the structure of nicotinamide and resulted in the identification and widespread use of benzamide analogs as PARP inhibitors. Recent searches for more potent and specific PARP inhibitors, facilitated by the crystal structure of the catalytic domain of PARP, led to several families of amide and lactam derivatives with multiple ring systems. New PARP inhibitors have shown efficacies in several animal disease models of cancer, ischemia and inflammation.