3',3'-cGAMP is a cyclic di-nucleotide produced by bacteria. 3',3'-cGAMP is also referred to as "canonical" cGAMP due the presence of the classical 3'-5' phosphodiester linkages between the guanosine and the adenosine.Recently, 3',3'-cGAMP was reported to bind STING (stimulator of IFN genes) and subsequently induce TBK1-IRF3-dependent production of IFN-β. Studies in bacteria revealed that 3',3'-cGAMP serves as a second messenger and plays a role in bacterial chemotaxis and colonization.Structural and functional studies revealed that the canonical 3',3'-cGAMP produced by bacteria is distinct from the noncanonical 2',3'-cGAMP produced by mammalian cGAS. Certain variants of STING are able to distinguish between canonical and noncanonical cGAMP.