This review discusses the mechanisms of polymyxin resistance in Gram-negative bacteria, both acquired and intrinsic. Polymyxins, polycationic antimicrobial peptides, are used as last-resort antibiotics for treating multidrug-resistant infections. The reintroduction of polymyxins has led to an increase in reports of resistance among Gram-negative bacteria, particularly in species like *Klebsiella pneumoniae*, *Pseudomonas aeruginosa*, and *Acinetobacter baumannii*. The review highlights the various strategies bacteria employ to protect themselves from polymyxins, including modifications of lipopolysaccharides (LPS), use of efflux pumps, capsule formation, and overexpression of the outer membrane protein OprH. Specific mechanisms such as the cationic substitution of phosphate groups in lipid A with phosphoethanolamine (PEN) and 4-amino-4-deoxy-L-arabinose (L-Ara4N) are detailed, along with the role of two-component systems (TCSs) like PhoP/PhoQ and PmrA/PmrB in regulating these modifications. The review also discusses the fitness costs associated with polymyxin resistance, including reduced virulence and invasiveness. Understanding these mechanisms is crucial for developing new strategies to combat polymyxin resistance.This review discusses the mechanisms of polymyxin resistance in Gram-negative bacteria, both acquired and intrinsic. Polymyxins, polycationic antimicrobial peptides, are used as last-resort antibiotics for treating multidrug-resistant infections. The reintroduction of polymyxins has led to an increase in reports of resistance among Gram-negative bacteria, particularly in species like *Klebsiella pneumoniae*, *Pseudomonas aeruginosa*, and *Acinetobacter baumannii*. The review highlights the various strategies bacteria employ to protect themselves from polymyxins, including modifications of lipopolysaccharides (LPS), use of efflux pumps, capsule formation, and overexpression of the outer membrane protein OprH. Specific mechanisms such as the cationic substitution of phosphate groups in lipid A with phosphoethanolamine (PEN) and 4-amino-4-deoxy-L-arabinose (L-Ara4N) are detailed, along with the role of two-component systems (TCSs) like PhoP/PhoQ and PmrA/PmrB in regulating these modifications. The review also discusses the fitness costs associated with polymyxin resistance, including reduced virulence and invasiveness. Understanding these mechanisms is crucial for developing new strategies to combat polymyxin resistance.