Pore-forming proteins (PFPs), involved in host-pathogen interactions, are produced as soluble, generally monomeric, proteins. To convert from the soluble to the transmembrane form, PFPs assemble, in the vicinity of the target membrane, into ring-like structures, which expose sufficient hydrophobicity to drive spontaneous bilayer insertion. Recent findings have highlighted two interesting aspects: (1) that pores form via similar overall mechanisms even if originating from vastly different structures and (2) specific folds found in PFPs can be found in widely different organisms, as distant as prokaryotes and mammals, highlighting that pore formation is an ancient form of attack that has been remarkably conserved.