The outer membrane (OM) of Gram-negative bacteria is a significant barrier to the entry of many harmful agents, including antibiotics. The OM is impermeable to macromolecules and allows only limited diffusion of hydrophobic substances through its lipopolysaccharide (LPS)-covered surface. The OM's integrity is maintained by the binding of cations to LPS, which forms a stable "tiled roof" structure. However, this structure can be disrupted by polycationic antibiotics like polymyxins, which bind avidly to LPS and disorganize the OM. Other cationic agents, such as lysine polymers and protamine, also have notable OM-damaging actions. These agents are useful tools in cellular studies and may have therapeutic applications in widening the spectrum of clinically used antibiotics. The review discusses various cationic agents that permeabilize the OM, including polymyxins, lysine polymers, and other cationic peptides. Polymyxins, such as polymyxin B nonapeptide (PMBN), are effective OM-permeabilizers and bactericidal agents. PMBN binds to LPS and increases the permeability of the OM to hydrophobic compounds, sensitizing bacteria to antibiotics. Other cationic peptides, like defensins, cecropins, magainins, and melittin, also have OM-permeabilizing properties but are less potent compared to polymyxins. The molecular mechanisms of OM permeability increase are not fully understood but involve alterations in the supramolecular structure of LPS. Cationic agents can disorder the quasicrystalline structure of LPS, enhancing lateral diffusion and allowing hydrophobic solutes to diffuse through the OM. Bacterial strains resistant to OM-permeabilizing agents, such as the pmarA mutants of *S. typhimurium* and polymyxin-resistant isolates of *E. coli*, have altered LPS structures that reduce binding to cationic agents. The OM-permeabilizing effect of cationic agents is inhibited by divalent cations, which compete for binding sites on LPS. Monovalent cations also have a competitive effect, but some cationic agents, like PMBN, are less sensitive to inhibition by monovalent cations. The review also discusses the use of various probes in OM permeabilizer studies, including lysozyme, hydrophobic antibiotics, periplasmic enzymes, and fluorescent hydrophobic probes. These probes help in assessing the effectiveness of different agents in permeabilizing the OM.The outer membrane (OM) of Gram-negative bacteria is a significant barrier to the entry of many harmful agents, including antibiotics. The OM is impermeable to macromolecules and allows only limited diffusion of hydrophobic substances through its lipopolysaccharide (LPS)-covered surface. The OM's integrity is maintained by the binding of cations to LPS, which forms a stable "tiled roof" structure. However, this structure can be disrupted by polycationic antibiotics like polymyxins, which bind avidly to LPS and disorganize the OM. Other cationic agents, such as lysine polymers and protamine, also have notable OM-damaging actions. These agents are useful tools in cellular studies and may have therapeutic applications in widening the spectrum of clinically used antibiotics. The review discusses various cationic agents that permeabilize the OM, including polymyxins, lysine polymers, and other cationic peptides. Polymyxins, such as polymyxin B nonapeptide (PMBN), are effective OM-permeabilizers and bactericidal agents. PMBN binds to LPS and increases the permeability of the OM to hydrophobic compounds, sensitizing bacteria to antibiotics. Other cationic peptides, like defensins, cecropins, magainins, and melittin, also have OM-permeabilizing properties but are less potent compared to polymyxins. The molecular mechanisms of OM permeability increase are not fully understood but involve alterations in the supramolecular structure of LPS. Cationic agents can disorder the quasicrystalline structure of LPS, enhancing lateral diffusion and allowing hydrophobic solutes to diffuse through the OM. Bacterial strains resistant to OM-permeabilizing agents, such as the pmarA mutants of *S. typhimurium* and polymyxin-resistant isolates of *E. coli*, have altered LPS structures that reduce binding to cationic agents. The OM-permeabilizing effect of cationic agents is inhibited by divalent cations, which compete for binding sites on LPS. Monovalent cations also have a competitive effect, but some cationic agents, like PMBN, are less sensitive to inhibition by monovalent cations. The review also discusses the use of various probes in OM permeabilizer studies, including lysozyme, hydrophobic antibiotics, periplasmic enzymes, and fluorescent hydrophobic probes. These probes help in assessing the effectiveness of different agents in permeabilizing the OM.