Peptidoglycan (murein) is a unique and essential structural component of the bacterial cell wall, forming a closed, bag-shaped structure around the cytoplasmic membrane. It consists of glycan strands cross-linked by short peptides, with variations in composition and sequence among different species. The structure of peptidoglycan varies with growth conditions and is influenced by factors such as the type of peptide stem, glycan strand composition, and cross-linking patterns. The peptide stem varies in amino acid composition, with some species showing unique variations, such as the presence of diamino acids or non-protein amino acids. The cross-linking of glycan strands occurs between specific amino acid residues, and the type of cross-linkage can differ between species. The thickness, elasticity, and porosity of peptidoglycan are important biophysical properties, with variations observed in different bacterial species. The structure of peptidoglycan is also influenced by environmental conditions, such as growth phase and medium composition. The sacculus is a dynamic structure that can change in response to environmental stress, and its architecture is crucial for bacterial survival and adaptation. Understanding the structural and functional diversity of peptidoglycan is essential for elucidating bacterial cell wall biology and for developing new antibiotics. The review summarizes the current knowledge on the chemical structure, biophysical properties, and variability of peptidoglycan in different bacterial species, highlighting the importance of structural variations in bacterial cell wall function and adaptation.Peptidoglycan (murein) is a unique and essential structural component of the bacterial cell wall, forming a closed, bag-shaped structure around the cytoplasmic membrane. It consists of glycan strands cross-linked by short peptides, with variations in composition and sequence among different species. The structure of peptidoglycan varies with growth conditions and is influenced by factors such as the type of peptide stem, glycan strand composition, and cross-linking patterns. The peptide stem varies in amino acid composition, with some species showing unique variations, such as the presence of diamino acids or non-protein amino acids. The cross-linking of glycan strands occurs between specific amino acid residues, and the type of cross-linkage can differ between species. The thickness, elasticity, and porosity of peptidoglycan are important biophysical properties, with variations observed in different bacterial species. The structure of peptidoglycan is also influenced by environmental conditions, such as growth phase and medium composition. The sacculus is a dynamic structure that can change in response to environmental stress, and its architecture is crucial for bacterial survival and adaptation. Understanding the structural and functional diversity of peptidoglycan is essential for elucidating bacterial cell wall biology and for developing new antibiotics. The review summarizes the current knowledge on the chemical structure, biophysical properties, and variability of peptidoglycan in different bacterial species, highlighting the importance of structural variations in bacterial cell wall function and adaptation.