Acinetobacter baumannii is a Gram-negative bacterium that causes hospital-acquired infections including ventilator-associated pneumonia, bacteraemia and urinary tract infections. Type VI secretion systems (T6SS) are macromolecular machines produced by many bacteria that play important roles in interbacterial competition and/or virulence. Many A. baumannii strains express a T6SS that is important for killing competitor bacteria but none of the T6SS toxins have yet been identified. T6SS toxins are often delivered together with the T6SS VgrG tip proteins. Analysis of the A. baumannii AB307 genome identified three vgrG genes, each of which was located upstream of putative toxin and immunity genes. To assess toxic activity, each putative toxin gene (rhs1, rhs2 and lysM) was cloned independently into the arabinose inducible E. coli plasmid pBAD-30. E. coli strains containing each construct were viable when gene expression was repressed, but not when expression was induced. To determine the role of each VgrG protein in toxin delivery, we generated vgrG1, vgrG2 and vgrG3 mutants and performed competition assays using AB307 wild-type or vgrG mutants as the predators and A. baylyi as the prey. As each of the single vgrG mutants was predicted to deliver two toxins, we also cloned pairs of immunity genes into the Acinetobacter plasmid pWH1266 and used these to transform A. baylyi, effectively giving these prey strains protection against two toxins. The wild-type AB307 strain and all the single vgrG mutants were able to kill A. baylyi containing empty pWH1266. However, the vgrG1 mutant (predicted to deliver Rhs2 and LysM but not Rhs1) was unable to kill A. baylyi expressing the Rhs2I and LysMI immunity proteins, but could kill A. baylyi containing pwH1266 or pWH1266 expressing the other pairs of immunity proteins. Similar results were obtained for the vgrG2 and vgrG3 mutants. Therefore, Rhs1, Rhs2 and LysM are T6SS-delivered antibacterial toxins, each toxin is specifically secreted by one VgrG protein, and Rhs1I, Rhs2I and LysMI are cognate immunity proteins specific for each toxin.