A range of genetical and physiological experiments have established that diverse bacterial cells possess a function called nucleoid occlusion, which acts to prevent cell division in the vicinity of the nucleoid. We have identified a specific effector of nucleoid occlusion in Bacillus subtilis, Noc (YyaA), as an inhibitor of division that is also a nonspecific DNA binding protein. Under various conditions in which the cell cycle is perturbed, Noc prevents the division machinery from assembling in the vicinity of the nucleoid. Unexpectedly, cells lacking both Noc and the Min system (which prevents division close to the cell poles) are blocked for division, apparently because they establish multiple nonproductive accumulations of division proteins. The results help to explain how B. subtilis specifies the division site under a range of conditions and how it avoids catastrophic breakage of the chromosome by division through the nucleoid.