Chitosan, a hydrophilic polysaccharide derived from chitin, exhibits broad antimicrobial activity against gram-negative and gram-positive bacteria and fungi. This review discusses three accepted antimicrobial mechanisms of chitosan: 1) ionic surface interaction leading to cell membrane disruption and leakage; 2) inhibition of mRNA and protein synthesis by penetration into microbial nuclei; and 3) formation of an external barrier that chelates metals and inhibits nutrient absorption. The effectiveness of chitosan is influenced by its molecular weight (MW) and degree of acetylation (DA), with lower MW and DA generally resulting in higher antimicrobial activity. Water-soluble chitosan derivatives, obtained through chemical modifications, enhance its applicability and antimicrobial activity. The review also highlights the varying sensitivity of microorganisms to chitosan, with some studies suggesting greater activity against gram-positive bacteria, while others indicate higher sensitivity in gram-negative bacteria. Overall, chitosan's antimicrobial properties make it a promising material for various applications, including food preservation and medical uses.Chitosan, a hydrophilic polysaccharide derived from chitin, exhibits broad antimicrobial activity against gram-negative and gram-positive bacteria and fungi. This review discusses three accepted antimicrobial mechanisms of chitosan: 1) ionic surface interaction leading to cell membrane disruption and leakage; 2) inhibition of mRNA and protein synthesis by penetration into microbial nuclei; and 3) formation of an external barrier that chelates metals and inhibits nutrient absorption. The effectiveness of chitosan is influenced by its molecular weight (MW) and degree of acetylation (DA), with lower MW and DA generally resulting in higher antimicrobial activity. Water-soluble chitosan derivatives, obtained through chemical modifications, enhance its applicability and antimicrobial activity. The review also highlights the varying sensitivity of microorganisms to chitosan, with some studies suggesting greater activity against gram-positive bacteria, while others indicate higher sensitivity in gram-negative bacteria. Overall, chitosan's antimicrobial properties make it a promising material for various applications, including food preservation and medical uses.