ABSTRACT Bis-(3′-5′)-cyclic dimeric GMP (c-di-GMP) is an intracellular second messenger that regulates adaptation processes, including biofilm formation, motility, and virulence in Gram-negative bacteria. In this study, we have characterized the core components of a c-di-GMP signaling pathway in the model Gram-positive bacterium Bacillus subtilis . Specifically, we have directly identified and characterized three active d i g uanylate c yclases, DgcP, DgcK, and DgcW (formerly YtrP, YhcK, and YkoW, respectively), one active c-di-GMP p hospho d i e sterase, PdeH (formerly YuxH), and a cyclic- d i g uanylate (c-di-GMP) r eceptor, DgrA (formerly YpfA). Furthermore, elevation of c-di-GMP levels in B. subtilis led to inhibition of swarming motility, whereas biofilm formation was unaffected. Our work establishes paradigms for Gram-positive c-di-GMP signaling, and we have shown that the concise signaling system identified in B. subtilis serves as a powerful heterologous host for the study of c-di-GMP enzymes from bacteria predicted to possess larger, more-complex signaling systems.