DNA damage by agents in the environment poses a constant threat to the survival of all organisms. In order to maintain the integrity of their genetic material, cells respond to such damage by activating, or inducing, a large repertory of enzymes that repair DNA and otherwise provide for cellular survival. Exposure of bacteria to DNA damaging agents results in the induction of a diverse set of physiological responses, collectively called the SOS response, which include enhanced capacity for recombinational repair, enhanced capacity for excision repair, enhanced mutagenesis, prophage induction, and inhibition of cell division. The research in our laboratory focuses on the SOS response in the bacterium Bacillus subtilis, a close cousin of the anthrax bacterium. Using a genomic screen, coupled with biochemical studies and microarray analyses, we have identified about forty genes that comprise the B. subtilis SOS response. Using a combination of genetic, proteomic, and biochemical analyses we are trying to understand how the integrated activities of the SOS gene products provide for the cell’s response to DNA damage.