The T6SS is a multiprotein complex that bacteria primarily use to kill competitors. It is present in many Gram-negative species and is composed of a baseplate, membrane-linked stabilizing structure, contractile sheath, and injectable needle. The needle is composed of stacked Hcp hexamers and is tipped by three VgrG proteins and a PAAR protein. Secreted effectors are commonly delivered via non-covalent interaction with one of the needle proteins. Acinetobacter baumannii is an important cause of hospital acquired infections. Many strains produce a T6SS, which acts to kill competing bacteria. We have characterised the breadth of effector functions delivered by the A. baumannii T6SS, how the system is regulated and how effectors are delivered. We analysed ~100 A. baumannii genomes and identified 33 families of effectors, including predicted DNases, RNases, peptidoglycan hydrolases, lipases, and >10 families with no clear functions. These proteins form a diverse set for identification of novel antibacterial functions and prey cell targets. We have focussed on the detailed characterisation of the T6SS in strain AB307 that delivers three antibacterial toxins, a DNase (Tde16), a peptidoglycan hydrolase (Tae17) and an effector of unknown function (Tse15). Each of these is delivered through non-covalent interaction with a specific VgrG protein (VgrG16, VgrG17, VgrG15, respectively). We have dissected the protein-protein interactions between Tse15/VgrG15 and Tae17/VgrG17. Using bacterial two hybrid assays, deletion constructs and domain swaps, we showed that the N-terminal ~50-100 amino acids of each VgrG interacted with the N-terminal regions of their cognate effectors. We then used scanning alanine mutagenesis of VgrG17 to identify two amino acids essential for Tae17 delivery; the first time such specific interactions have been observed for effector delivery. Single amino acid substitutions in VgrG15 failed to identify specific essential residues, suggesting more than a single interacting region. Understanding the specific determinants of effector delivery will, in future, allow us to manipulate the system for delivery of different sets of effectors and even our own user-designed proteins.