In Escherichia coli, spatiotemporal control of cell division occurs at the level of the assembly/disassembly process of the essential cytoskeletal protein FtsZ. A number of regulators interact with FtsZ and modulate the dynamics of the assembled FtsZ ring at the midcell division site. In this article, we report the identification of an FtsZ stabilizer, ZapC (Z-associated protein C), in a protein localization screen conducted with E. coli. ZapC colocalizes with FtsZ at midcell and interacts directly with FtsZ, as determined by a protein-protein interaction assay in yeast. Cells lacking or overexpressing ZapC are slightly elongated and have aberrant FtsZ ring morphologies indicative of a role for ZapC in FtsZ regulation. We also demonstrate the ability of purified ZapC to promote lateral bundling of FtsZ in a sedimentation reaction visualized by transmission electron microscopy. While ZapC lacks sequence similarity with other nonessential FtsZ regulators, ZapA and ZapB, all three Zap proteins appear to play an important role in FtsZ regulation during rapid growth. Taken together, our results suggest a key role for lateral bundling of the midcell FtsZ polymers in maintaining FtsZ ring stability during division.