Poly(ADP-ribose) polymerase 1 (PARP1) is an abundant nuclear protein that plays an important role in repairing DNA and responding to infection. Here we review recent evidence that PARP1 and related proteins also carry out crucial functions regulating genes during normal development. Genetic studies in mammals and Drosophila have implied that PARPs mediate rapid responses to environmental stimuli, including infection, stress, hormones, and growth signals. In addition, these polymerases may control fundamental processes that differentially mold and remodel chromatin within the many cell types of a developing embryo. We discuss a unified mechanism of PARP action during DNA repair, gene transcription, and chromatin modulation.