The bacterial cell envelope is a complex, multilayered structure that protects bacteria from their environment. It consists of two major groups: Gram-negative and Gram-positive. Gram-negative bacteria have a thin peptidoglycan cell wall surrounded by an outer membrane containing lipopolysaccharide, while Gram-positive bacteria lack an outer membrane but have thicker layers of peptidoglycan with teichoic acids threading through them. The composition and organization of these layers, as well as the mechanisms of cell envelope assembly, are discussed. The outer membrane, composed of glycolipids and lipoproteins, serves as a protective barrier and contains essential enzymes. The peptidoglycan cell wall provides rigidity and shape to the cell. The periplasm, a dense aqueous compartment, houses proteins involved in compartmentalization and reactions. The inner membrane, a phospholipid bilayer, performs functions similar to those of eukaryotic organelles. Transenvelope machines, such as flagella and efflux pumps, span the peptidoglycan and are located in all compartments. Envelope biogenesis involves the synthesis and translocation of components from the cytoplasm or across the inner membrane. Chaperones like SurA, Skp, and DegP assist in the assembly of outer membrane proteins. Lipoproteins are delivered to the outer membrane by the Lol system. LPS and phospholipids are synthesized on the inner leaflet of the inner membrane and flipped to the outer leaflet. The Gram-positive cell envelope differs from the Gram-negative in the absence of an outer membrane and the presence of teichoic acids, which contribute to cell wall structure and function. The cell envelopes of Corynebacterineae, including *Mycobacterium*, have characteristics of both Gram-positive and Gram-negative bacteria, with a symmetrical outer membrane and unique mycolic acids. The complex and dynamic nature of bacterial cell envelopes plays crucial roles in protection and adaptation to environmental conditions.The bacterial cell envelope is a complex, multilayered structure that protects bacteria from their environment. It consists of two major groups: Gram-negative and Gram-positive. Gram-negative bacteria have a thin peptidoglycan cell wall surrounded by an outer membrane containing lipopolysaccharide, while Gram-positive bacteria lack an outer membrane but have thicker layers of peptidoglycan with teichoic acids threading through them. The composition and organization of these layers, as well as the mechanisms of cell envelope assembly, are discussed. The outer membrane, composed of glycolipids and lipoproteins, serves as a protective barrier and contains essential enzymes. The peptidoglycan cell wall provides rigidity and shape to the cell. The periplasm, a dense aqueous compartment, houses proteins involved in compartmentalization and reactions. The inner membrane, a phospholipid bilayer, performs functions similar to those of eukaryotic organelles. Transenvelope machines, such as flagella and efflux pumps, span the peptidoglycan and are located in all compartments. Envelope biogenesis involves the synthesis and translocation of components from the cytoplasm or across the inner membrane. Chaperones like SurA, Skp, and DegP assist in the assembly of outer membrane proteins. Lipoproteins are delivered to the outer membrane by the Lol system. LPS and phospholipids are synthesized on the inner leaflet of the inner membrane and flipped to the outer leaflet. The Gram-positive cell envelope differs from the Gram-negative in the absence of an outer membrane and the presence of teichoic acids, which contribute to cell wall structure and function. The cell envelopes of Corynebacterineae, including *Mycobacterium*, have characteristics of both Gram-positive and Gram-negative bacteria, with a symmetrical outer membrane and unique mycolic acids. The complex and dynamic nature of bacterial cell envelopes plays crucial roles in protection and adaptation to environmental conditions.