(p)ppGpp is a well known intracellular signal that mediates bacterial stringent response to environment stresses through the change of its concentration level thus controls many important cellular processes for bacterial survival. In this review, we outline the mechanism of (p)ppGpp action, the enzyme system involved in (p)ppGpp metabolism, and summarize the signal transmission, the regulation and the diversity of (p)ppGpp metabolism. Moreover, we give a brief introduction on our achieved results recently about (p)ppGpp metabolism in cyanobacteria, and predict that a (p)ppGpp new metabolic mechanism different from those known exists in cyanobacteria.