Bacteriophages and phage tail-like bacteriocins (PTLBs) rely on receptor-binding proteins (RBPs) located in tail fibers or spikes for an initial and specific interaction with susceptible bacteria. Bacteriophages kill bacteria through a lytic, replicative cycle, whereas PTLBs kill the target through membrane depolarization in a single hit mechanism. Extensive efforts in the engineering of RBPs of both phages and PTLBs have been undertaken to obtain a greater understanding of the structural organization of RBPs. In addition, a major goal of engineering RBPs of phages and PTLBs is the production of antibacterials with a customized spectrum. Swapping of the RBP of phages and PTLBs results in a shift in activity spectrum in accordance with the spectrum of the new RBP. The engineering of strictly virulent phages with new RBPs required significant technical advances in the past decades, whereas the engineering of RBPs of PTLBs relied on the traditional molecular techniques used for the manipulation of bacteria and was thus relatively straightforward. While phages and PTLBs share their potential for specificity tuning, specific features of phages such as their lytic killing mechanism, their self-replicative nature and thus different pharmacokinetics and their potential to co-evolve are clear differentiators compared with PTLBs in terms of their antibacterial use.