The bacterial cell envelope is a complex, multilayered structure that protects bacteria from their environment. Gram-negative bacteria have a thin peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharide (LPS), while Gram-positive bacteria have thick peptidoglycan layers without an outer membrane. Teichoic acids, long anionic polymers, thread through these layers. The cell envelope is essential for survival, providing protection and selective permeability. It consists of multiple layers, including the outer membrane (OM), peptidoglycan cell wall, and inner membrane (IM), with the periplasmic space between them. The OM contains lipopolysaccharide, which is crucial for bacterial survival and immune recognition. The peptidoglycan layer provides structural integrity, and its thickness varies between Gram-negative and Gram-positive bacteria. The OM is essential for Gram-negative bacteria, containing proteins like porins that allow the passive diffusion of small molecules. The peptidoglycan is synthesized in the cytoplasm and translocated across the inner membrane. The OM and peptidoglycan are assembled through complex processes involving translocon proteins, chaperones, and other molecular machines. The cell envelope of Gram-positive bacteria lacks an outer membrane but contains teichoic acids, which are anionic polymers that contribute to the structure and function of the cell wall. The cell envelope of Corynebacterineae, including Mycobacteria, has unique features, such as arabinogalactan and mycolic acids, which contribute to their resistance to staining and environmental stress. The cell envelope is dynamic and plays a critical role in bacterial survival, adaptation, and pathogenesis. Understanding the assembly and regulation of these complex structures is a major challenge in bacterial biology.The bacterial cell envelope is a complex, multilayered structure that protects bacteria from their environment. Gram-negative bacteria have a thin peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharide (LPS), while Gram-positive bacteria have thick peptidoglycan layers without an outer membrane. Teichoic acids, long anionic polymers, thread through these layers. The cell envelope is essential for survival, providing protection and selective permeability. It consists of multiple layers, including the outer membrane (OM), peptidoglycan cell wall, and inner membrane (IM), with the periplasmic space between them. The OM contains lipopolysaccharide, which is crucial for bacterial survival and immune recognition. The peptidoglycan layer provides structural integrity, and its thickness varies between Gram-negative and Gram-positive bacteria. The OM is essential for Gram-negative bacteria, containing proteins like porins that allow the passive diffusion of small molecules. The peptidoglycan is synthesized in the cytoplasm and translocated across the inner membrane. The OM and peptidoglycan are assembled through complex processes involving translocon proteins, chaperones, and other molecular machines. The cell envelope of Gram-positive bacteria lacks an outer membrane but contains teichoic acids, which are anionic polymers that contribute to the structure and function of the cell wall. The cell envelope of Corynebacterineae, including Mycobacteria, has unique features, such as arabinogalactan and mycolic acids, which contribute to their resistance to staining and environmental stress. The cell envelope is dynamic and plays a critical role in bacterial survival, adaptation, and pathogenesis. Understanding the assembly and regulation of these complex structures is a major challenge in bacterial biology.