Physiological activities attributed to bacterial plasma membranes are outlined. The chemical composition of bacterial plasma membranes is discussed and the contribution of lipids, phospholipids, squalene, hopanoid, carotenoids, quinones, and lipopolysaccharides is presented. An overview of transmembrane activities of proteins and electron transport proteins is reviewed. A discussion of electron carrier complexes and types of ATP synthases is provided. Specific attention is given to membrane systems of cell wall-less prokaryotes, bacteriophage, magnetosomes, anammoxosomes, and photosynthetic membranes. Unique membrane structures are examined and include plasma membrane vesicles and laminated membranes in nitrifying bacteria. Lipid synthesis and membrane homeostasis in bacteria are reviewed. The physiological significance of maintaining membrane fluidity and asymmetry is explored. A discussion of membrane destabilization includes the impact of enzymes, antibiotics, and specific chemicals.